144 Fun Facts About Pi Day

Which British single-board computer put its 3 Model B+ on sale on Pi Day 2018?

Raspberry Pi began as a cheap board meant to get schoolchildren programming, and its $35 3 Model B+ went on sale on March 14, 2018.

Using pi, the volume of a cylinder with radius z and height a spells out which food?

Pizza: a cylinder's volume is pi times the radius squared times the height, so a radius of z and a height of a give pi·z·z·a, a well-worn maths joke.

Pi is the ratio of a circle's circumference to its what?

Diameter is the key: wrap a string once around any round object, cut it into lengths that span the middle, and you get three pieces plus a small leftover every time.

What type of number is pi?

Irrational means no fraction ever equals pi exactly, so its decimals never end or fall into a repeating loop, and record hunters can keep computing fresh digits forever.

What is the formula for the circumference of a circle?

2πr is pi's definition rearranged: the distance around a circle is pi times the distance straight across it, and straight across is two radii, which is where the 2 comes from.

What is the formula for the area of a circle?

πr² appears when you slice a circle into thin wedges and lay them head to tail: they form a near-rectangle one radius high and half the circumference long.

Which famous physicist's birthday falls on Pi Day?

Albert Einstein was born in the city of Ulm in 1879, and the longest-running Pi Day party includes a round of 'Happy Birthday' sung in his honour.

Which space agency sets students a Pi Day Challenge built on maths from its real missions?

NASA's challenge poses the kind of problems its engineers solve with pi, such as aiming a laser signal from deep space at the spot where Earth will be when it arrives.

Which state legislature nearly passed an 1897 bill implying pi equals 3.2?

Indiana was saved by chance: a Purdue mathematics professor happened to be at the statehouse, was shown the bill and coached the senators, who shelved it.

Which legislative body passed a 2009 resolution supporting the designation of National Pi Day?

The U.S. House approved the resolution in March 2009; it urges schools to use the day to teach students about pi and draw them into mathematics.

Who organized the first large-scale Pi Day celebration in 1988?

Larry Shaw went on hosting the celebration every year until his death in 2017, and colleagues fondly called him the Prince of Pi.

At which museum was the first Pi Day celebration held?

The San Francisco Exploratorium's staff came up with the holiday at an off-site retreat in 1988, and it grew into a yearly tradition at the museum.

Which ancient Greek mathematician is famous for his method of approximating pi using polygons?

Archimedes inscribed and circumscribed regular polygons around a circle, doubling their sides step by step, and squeezed pi between the bounds 223/71 and 3 1/7.

Which Simpsons character silences a rowdy science conference by shouting that pi is exactly three?

Professor Frink is struggling to quiet the hall while Lisa waits in the wings to present her discovery of why bullies pick on nerds.

How many degrees are there in π radians?

180 degrees is a half turn, or π radians; mathematicians favour radians because the calculus of sine and cosine only comes out clean when angles are measured that way.

Which country writes dates month-first, the format that makes 3/14 Pi Day?

The United States writes dates month-first, so March 14 becomes 3/14; day-first countries such as the United Kingdom would write 14/3, which is why some mark July 22 (22/7) instead.

What does it mean that pi is a transcendental number?

Not the root of any rational polynomial: no algebra equation with fraction coefficients has pi as a solution. Almost all numbers are like this, yet proving it for any one of them is hard.

Which ancient civilization's clay tablet, more than 3,500 years old, treats pi as 3.125?

Babylonians usually made do with a plain 3; this tablet, dug up near Susa in 1936, shows they also knew the sharper 3 1/8, about half a percent below the true value.

On Pi Day 2015 at 9:26:53 AM, what did the date and time together spell out?

This 'Pi Instant' comes around once a century, and 2015 was billed as Super Pi Day because that year's date supplied five digits.

What is the hobby of memorizing digits of pi called, a pun on the study of language?

Piphilology blends 'pi' with 'philology'; devotees even write poems, called piems, in which each word's letter count gives the next digit.

Which Indian mathematician's c.1400 infinite series for pi predated Europe's by over two centuries?

Madhava's own mathematical writings are lost; the series survives only because later scholars of his Kerala school credited it to him, long before Gregory and Leibniz found it again.

The Comte de Buffon, whose probability puzzle is a classic way to estimate pi, was chiefly famous as what?

A naturalist above all, Buffon spent four decades on his Histoire Naturelle, publishing 36 volumes that tried to describe the whole living world.

The ancient Greek who trapped pi between 96-sided polygons began his doubling from which shape?

A hexagon was the natural start because its perimeter is easy to work out; four doublings later, at 96 sides, he had pinned pi between 223/71 and 22/7.

Which ancient geometry challenge was proved impossible in 1882, once pi was shown to be transcendental?

Squaring the circle means building a square with exactly a circle's area using only compass and straightedge; the phrase lives on as a byword for attempting the impossible.

The "tau movement" argues that which number should replace pi as the fundamental circle constant?

2π (approximately 6.283) is one full turn in radians, so with tau a quarter turn is simply a quarter of tau; its fans celebrate on June 28, written 6/28.

What is Euler's identity, often called the most beautiful equation in mathematics?

e^(iπ) + 1 = 0 came top when mathematicians rated formulas inside a brain scanner in 2014: the ones they found beautiful lit up the same emotional region as great art and music.

In 1949 John von Neumann's team spent 70 hours computing 2,037 digits of pi on which computer?

ENIAC was the first electronic computer ever used to compute pi, and in under three days it nearly doubled the best total people had reached in over 2,000 years of trying.

Which Indian mathematician produced pi formulas that converge extremely rapidly?

Srinivasa Ramanujan's 1914 paper gave series for 1/π that add roughly eight correct digits per term, anticipating the fast algorithms used for record computations decades later.

Which university has often timed its admissions decision letters to arrive on Pi Day?

MIT has released its undergraduate admissions decisions on March 14 for years; in 2015 they went online at 9:26 am, that year's 'pi minute'.

Which mathematician brothers' formula, adding about 14 digits per term, carried pi past a billion digits in 1989?

The Chudnovsky brothers, David and Gregory, later built their own supercomputer in a Manhattan apartment and passed two billion digits on it.

The Comte de Buffon's 18th-century pi-estimating probability problem involves dropping what onto parallel strips?

A needle lands at a random angle, and averaging over every possible angle brings the circle in: one as long as the strips are wide crosses a line 2/π of the time, about 64 percent.

Which widely used statistical distribution carries pi under a square root in its formula?

The normal distribution's bell curve encloses an area of exactly the square root of two pi before scaling, so its formula divides by that amount to make the probabilities add up to one.

Which mathematician, also remembered for a map projection, first proved in the 1760s that pi cannot be written as a fraction?

Johann Heinrich Lambert was a tailor's son who had to leave school at twelve and taught himself mathematics in his spare hours.

Ferdinand von Lindemann, who proved pi transcendental in 1882, later supervised which giant of modern mathematics?

David Hilbert took his doctorate under Lindemann at Königsberg in 1885 and went on to set the list of 23 unsolved problems that steered twentieth-century mathematics.

What can the 1995 Bailey–Borwein–Plouffe formula for pi do?

It can find a far-off binary digit directly: the PiHex project used a variant to reach the quadrillionth binary digit of pi without computing any of the digits before it.

A run of six 9s in a row, 762 decimal places into pi, is named after which physicist?

Richard Feynman is said to have joked about reciting pi up to that point and ending 'nine nine nine nine nine nine and so on', though there is no record of when, or whether, he said it.

A famous worked example of why 15 decimals of pi are plenty uses a circle stretching beyond which far-flung spacecraft?

Voyager 1 is the most distant spacecraft, about 16 billion miles away in 2026; with 15 decimals, a circle even wider than that comes out wrong by only about half an inch.

For over 800 years from the 5th century, the most accurate value of pi belonged to a mathematician from which country?

China's Zu Chongzhi pinned pi between 3.1415926 and 3.1415927; the book that explained his method was later lost, so nobody knows quite how he did it.

Which fraction, found in the 5th century, approximates pi to six decimal places?

355/113 is freakishly good because the next step in pi's continued fraction is the unusually large 292; no fraction with a four-digit denominator comes closer.

Which English mathematician, who introduced the ∞ symbol, published an infinite product for pi in 1656?

John Wallis's product multiplies 2/1 × 2/3 × 4/3 × 4/5 and so on to reach half of pi; he first made his name cracking Royalist ciphers for Parliament in the English Civil War.

In Life of Pi, what is the main character's full first name, which he shortens to Pi?

Piscine Molitor Patel was named after a Paris swimming pool; after schoolmates turned it into 'Pissing' he rebranded himself as Pi.

What is the sum of the infinite series 1 - 1/3 + 1/5 - 1/7 + 1/9 - ...?

π/4 is the limit of this famously simple series, but it crawls there: after 500,000 terms it has pinned down only 5 decimal places of pi.

Which tech company's employee set the 2019 record for most digits of pi (31.4 trillion)?

Google's Emma Haruka Iwao computed exactly 31,415,926,535,897 digits, a count picked to echo pi's own opening digits, and the company announced the record on Pi Day 2019.

Which sentence encodes pi in its word lengths?

How I want a drink, alcoholic of course: count the letters, 3-1-4-1-5-9-2-6. Physicist James Jeans gets the credit, and his sentence goes on to blame quantum mechanics for the thirst.

Which famous scientist died on Pi Day in 2018?

Stephen Hawking died at 76, more than fifty years after doctors told him motor neurone disease would kill him within two years.

Euler showed that 1 + 1/4 + 1/9 + 1/16 + … adds up to exactly what?

π²/6, about 1.645: the puzzle is called the Basel problem after Euler's home town, where the Bernoulli family had tried and failed to crack it.

July 22, written 22/7 in day/month format, is celebrated as which unofficial maths holiday?

Pi Approximation Day honours 22/7, a fraction that is actually a closer match to pi than the 3.14 behind the March celebration.

Whose 707-digit hand calculation of pi, published in 1873, turned out to go wrong partway through?

William Shanks's slip went unnoticed for some seventy years, until a fresh computation in the 1940s exposed it, long after his death in 1882.

In 2015 Rajveer Meena spent nearly ten hours reciting pi from memory, a Guinness record of how many digits?

70,000 digits, about two every second for nearly ten hours, and Guinness notes that he wore a blindfold the whole time.

Which UN body designated Pi Day as the International Day of Mathematics in 2019?

UNESCO acted on a proposal led by the International Mathematical Union, which picked March 14 because many countries already celebrated it as Pi Day.

How was the first Pi Day marked in 1988?

Staff marched around a circular space, then ate fruit pies, at a small party its organiser dreamed up after a staff retreat as a way to pull colleagues together.

A university team in which Alpine country set a pi record of 62.8 trillion digits in 2021?

Switzerland's University of Applied Sciences of the Grisons needed 108 days, and at first revealed only the last ten digits while Guinness checked the claim.

Which pastry chef, creator of the Cronut, baked the pie in a 2018 Pi Day Doodle?

Dominique Ansel baked a salted caramel apple pie and laid the Doodle out as pi's own formula, a pie's circumference divided by the distance across it.

In 2014 some fans stretched Pi Day into what, by reading 3/14 another way?

Pi Month: read as month and year, 3/14 is March 2014, a match that comes only once a century, so some fans celebrated for all 31 days.

What is the volume of a sphere of radius r?

4/3πr³ is exactly two-thirds of the cylinder that just encloses the sphere, a result its ancient discoverer prized so much that he wanted the two shapes carved on his tomb.

In which director's 1966 thriller Torn Curtain is π the code name of an escape network?

Alfred Hitchcock has Paul Newman's professor scratch the symbol in the dirt with his foot, the sign that summons the underground network smuggling fugitives across the Iron Curtain to the West.

Which New Jersey town celebrates Pi Day as a joint birthday party for a famous physicist who lived there?

Princeton became the physicist's home in 1933: when the Nazis took power he gave up his German citizenship and crossed the Atlantic to join the Institute for Advanced Study.

Which maths YouTuber led hundreds of volunteers in calculating 139 digits of pi by hand in 2024?

Matt Parker called it the biggest hand calculation in a century; that August asteroid 314159, numbered with pi's first six digits, was named Mattparker.

About 61 percent of random whole-number pairs share no common factor; which expression gives that chance exactly?

6/π² appears because each prime p divides both numbers in one pair out of p², and multiplying the chances of escaping every prime gives exactly that value.

The 314th day of a common year, a second pi date for some, falls in which month?

November holds it: the ten months through October add up to 304 days, so day 314 is November 10, and in leap years it slips back to November 9.

Measured across, which set of circles covers the greatest total area?

One 18-inch circle wins because area grows with the square of the width: it beats two 12-inch circles by 81 to 72, so doubling a circle's width quadruples what fits inside.

In mathematical notation, what does the capital Greek letter Π (pi) stand for?

Repeated multiplication takes a capital Π because the result is called a product, just as a capital sigma, Σ, marks a sum.

Which physicist founded the Exploratorium in 1969?

Frank Oppenheimer was the younger brother of J. Robert Oppenheimer; blacklisted from physics in the McCarthy era, he spent years as a Colorado cattle rancher before opening the museum.

William Jones, the first mathematician to use π for the circle ratio, in 1706, came from which country?

Wales produced Jones, a charity-school boy from Anglesey who taught mathematics aboard Navy ships before his 1706 beginners' textbook introduced π.

The 1706 adoption of π followed earlier abbreviations of which Greek word?

Periphery, the Greek for circumference, was shortened to π by William Oughtred, who used the letter only as the top of a fraction, decades before π alone meant the ratio.

William Jones, who first used π for the circle ratio, was a close friend of Halley and which other giant?

Isaac Newton trusted Jones to edit and publish his manuscripts, beginning in 1711 with Newton's early, unpublished work on calculus.

Zacharias Dase, who computed 200 digits of pi in 1844, was later paid to tabulate what?

Factors of numbers: his native Hamburg funded Dase, a touring mental calculator, to list the factors of every number across several millions, a task still unfinished when he died in 1861.

In which law of electric force does the constant 1/(4πε₀) appear?

Coulomb's law gives the force between two charges as q₁q₂/(4πε₀r²); Charles-Augustin de Coulomb established it in 1785 by measuring the tiny twists of a torsion balance.

Zhang Heng and Brahmagupta, centuries apart, both took pi to be the square root of which whole number?

10 gives about 3.162, less than one percent too high; Zhang Heng reached it around 130 AD from a rule comparing a cube with the sphere that fits inside it.

Egypt's Rhind Papyrus is named after whom?

Its buyer was Alexander Henry Rhind, a Scot who purchased the scroll in Egypt in 1858. Its scribe, Ahmes, noted that he was only copying an older text; one of its rules puts pi near 3.16.

Around 150 AD, which astronomer of Alexandria gave 3.1416 for pi?

Ptolemy gave the value in his Almagest, probably taking it from his table of chords, which treats the circle as a polygon of 360 sides.

A rope around Earth's equator is lengthened by 2π metres, about 6.28; how high can it now hover all round?

About 1 metre: the answer is the same whatever the circle's size, so the same extra rope lifts a loop a metre off Earth or off a tennis ball.

Third-century mathematician Liu Hui settled on which fraction for pi, admitting it was 'a bit small'?

157/50 is pi cut off after two decimal places, which Liu Hui judged good enough for everyday work even though his own polygons had shown him that the true value sits slightly higher.

Which Indian astronomer, namesake of India's first satellite, used 3.1416 for pi in 499 AD?

Aryabhata gave the rule in verse: add four to 100, multiply by eight and add 62,000 for the circumference of a circle 20,000 across, a result he called only approximate.

Jamshid al-Kashi set a 16-digit pi record in 1424 in which Silk Road city?

Samarkand's ruler Ulugh Beg, an astronomer himself, invited al-Kashi to his new school there, where he worked the value out in base 60 and then converted it to decimals.

Pi pioneer François Viète cracked Spain's codes so well that its king accused him of using what?

Black magic was the Spanish king's only explanation when Viète, a lawyer in the service of France's Henry IV, kept reading his secret dispatches; in 1593 Viète also published an infinite product for pi.

Ludolph van Ceulen, who spent decades computing digits of pi, also taught which combat skill in Delft and Leiden?

Fencing paid his way: he taught it alongside mathematics in Delft and opened a fencing school in Leiden in 1594, six years before an engineering school there made him a professor.

William Brouncker, who found a continued fraction for pi, became the first president of which body?

The Royal Society's 1662 charter named Brouncker its first president, and he kept the chair for 15 years while also helping to run the Navy alongside the diarist Samuel Pepys.

In 1706 John Machin's fast-converging formula made him the first person to compute how many digits of pi?

100 digits fell to Machin's new formula, and William Jones announced the feat that same year in the very book that first used the symbol π.

In a classic pi mnemonic, 'May I have a large container of' which drink keeps the letter counts matching pi's digits?

Coffee has six letters, the digit needed after 3.141592, since the words before it run 3, 1, 4, 1, 5, 9 and 2 letters long.

The word 'radius' was the Latin name for which part of a wheel?

A spoke runs from hub to rim just as a radius runs from centre to edge; the same Latin word also meant a ray of light, which makes the English 'ray' its cousin.

Which of these everyday shapes has a volume formula containing pi squared?

A ring doughnut is a torus, a circle swept round in a circle, so pi enters its volume twice: once for the round cross-section and once for the loop it travels.

Nilakantha's Tantrasamgraha, the 1501 Sanskrit verse treatise that set down Kerala's infinite series, was chiefly a work on which science?

Astronomy was the point: the Kerala school hit on its infinite series while trying to solve astronomical problems, and the treatise's 432 verses mostly track the planets.

Whose 1837 result showed constructible lengths must solve certain polynomial equations?

Pierre Wantzel showed in 1837 that a constructible length must satisfy a polynomial whose degree is a power of two, settling angle trisection and cube doubling; the circle followed in 1882.

The 1882 theorem proving pi transcendental also establishes the transcendence of which constant?

e falls out at once: the theorem says e raised to any non-zero algebraic power is transcendental, and 1 is such a power, while pi takes one further step.

Which German mathematician's work underlies a pi algorithm that doubles its correct digits each step?

Carl Friedrich Gauss explored the arithmetic-geometric mean, a way of averaging two numbers over and over, long before computers existed; Richard Brent and Eugene Salamin each built the algorithm on it in the 1970s.

A tube holds exactly three stacked tennis balls; compared with its height, the distance around it is what?

Slightly longer: the height is three ball-widths but the distance around is pi ball-widths, so the tube is a little further round than it is tall, though it never looks it.

Shigeru Kondo's 2011 record of 10 trillion digits of pi was set, remarkably, on what?

One man's desktop computer, Kondo's own, ran for 371 days and survived several hard-drive failures, using Alexander Yee's program y-cruncher.

About 31 million seconds, close to π × 10⁷, make up roughly which span of time?

One year works out to 31,557,600 seconds, since each of its 365.25 days has 86,400, which lands within half a percent of π × 10⁷ by pure coincidence.

The exoplanet K2-315b was nicknamed 'Pi Earth' in 2020 because which measurement matches pi's digits?

Its year, in days: the Earth-sized planet circles a small, cool star so closely that one orbit takes about as many days as pi, and the discovery paper's title joked that it was 'served warm'.

For a circle of radius 2, how do the numbers for its area and its circumference compare?

They are equal, both 4π: radius 2 is the only size where the two numbers match, because the area pulls ahead as soon as the circle grows any bigger.

Mole Day, a Pi Day-style holiday observed on October 23 from 6:02 am, celebrates which science?

Chemistry's holiday honours Avogadro's number, 6.02 × 10²³, the count of particles in one mole of a substance, so it runs from 6:02 am to 6:02 pm on 10/23.

In geometry, what is the pie-slice region between two radii of a circle called?

A sector takes up the same share of the circle's area as its angle takes of a full turn, which is how a pie chart turns percentages into slices.

In 1973 a French team became the first to compute how many digits of pi?

1 million digits came when Jean Guilloud moved up to the faster CDC 7600, doubling the half-million he had reached on a CDC 6600 six years earlier.

Which 2010 book spells out 10,000 digits of pi in its word lengths?

Not A Wake has a 3-1-4 title of its own, and Mike Keith wrote each thousand digits in a different style, opening with a poem.

In Pilish, where each word's letter count gives a digit of pi, a ten-letter word stands for which digit?

0: no word has zero letters, so Pilish spends its ten-letter words on pi's zeros, the first of which sits 32 places after the decimal point.

Which Poe poem did Mike Keith retell in Pilish, opening 'Poe, E.'?

The Raven became 'Near a Raven', which encodes 740 digits; Keith later reused it, lightly altered, as the opening section of a story nearly 4,000 digits long.

About how many digits of pi are enough to work out the observable universe's circumference to within one atom's width?

40 or so is plenty: NASA's own figure is 38 digits for a circle 46 billion light-years in radius measured to the width of a hydrogen atom, because each extra digit cuts the error tenfold.

Which singer's 2005 song 'π' has her singing more than a hundred digits of pi?

Kate Bush sings pi to its 78th decimal place on her album Aerial, then skips ahead and carries on from the 101st to the 137th.

Which Purdue professor happened to be present and helped sink the Indiana pi bill?

Clarence Abiathar Waldo, a Purdue mathematics professor in town over the university's budget, briefed the senators; the Senate then postponed the bill indefinitely on February 12, 1897.

Which sign of the zodiac does Pi Day fall under?

Pisces runs from about February 19 to March 20, so Pi Day lands in its final week, days before Aries restarts the zodiac at the spring equinox.

The 1897 bill implying pi is 3.2 passed one state's House by what margin?

Unanimously, 67 to 0: the bill sailed through the House and was shelved in the Senate only after a visiting mathematics professor had explained it to the senators.

Which Greek capital letter looks just like a Latin P, even though P actually descends from pi?

Rho is written Ρ but sounds like an R, which is why the chi-rho, an early Christian monogram made from the first two letters of 'Christ' in Greek, looks like an X laid over a P.

The random-sampling method that estimates pi by scattering points is named after which gambling resort?

Monte Carlo is Monaco's casino district, a fitting name for a method that swaps exact calculation for thousands of random trials; Stanisław Ulam and Nicholas Metropolis published it under that title in 1949.

Stanisław Ulam devised a random-sampling way to estimate numbers such as pi while working at which laboratory in the 1940s?

Los Alamos National Laboratory had him back on nuclear weapons work in 1946, months after an illness left him wondering about his odds at solitaire and whether random trials could estimate them.

Yann Martel's Life of Pi won which literary award the year after its 2001 publication?

The Man Booker Prize had only just gained the first word of its name, because the investment firm Man Group became its sponsor in 2002, the year Life of Pi won.

Which solid has volume equal to one third of πr²h?

A cone holds exactly one third of the cylinder with the same base and height, so three cones of sand fill that cylinder to the brim.

Which director's 1998 debut, Pi, won the Directing Award at Sundance?

Darren Aronofsky and his producer raised the budget by asking friends and relatives for $100 each, with a promise of $150 back if the film ever made money.

Daniel Tammet, who recited 22,514 digits of pi on Pi Day 2004, says he experiences numbers as what?

Shapes and colours appear to Tammet for every number: two is a motion and five is a clap of thunder, he says, and multiplying means watching two shapes merge into a third.

Which principle of quantum physics is often written Δx·Δp ≥ h/4π?

The Heisenberg uncertainty principle picks up its 4π because physicists write the limit as ħ/2, and ħ is Planck's constant h divided by 2π.

What is the status of the claim that pi's digits turn up equally often?

Still unproven: the digits computed so far pass statistical tests for evenness, yet no one has managed to prove that the balance holds all the way through.

In which number base do pi's digits begin 3.243F6A88?

Base 16 borrows the letters A to F for the values ten to fifteen; the Blowfish cipher fills its starting tables with these digits because nobody could have rigged them.

The title word 'Cadaeic' in Mike Keith's pi story hides 3.141593 using its letters' what?

Alphabet positions: C, A, D, A, E, I, C are letters 3, 1, 4, 1, 5, 9 and 3, and one section of the story repeats the trick with the first letter of every sentence.

What was engraved on the tombstone of Ludolph van Ceulen, who spent decades computing pi?

His 35 digits of pi went onto the stone after his death in 1610, and for generations Germans called pi the Ludolphine number in his honour.

A famous Science paper claimed that the average winding ratio of which natural features equals pi?

Rivers were said to average pi when their true length is divided by the straight-line distance from source to mouth, but later studies found the real figure is below 2.

In which 1960s sci-fi series is a possessed computer tied up by an order to compute pi's last digit?

Star Trek's Spock gives the order in the 1967 episode 'Wolf in the Fold', knowing the sum can never finish because pi's digits go on forever.

The 35 digits of pi found by Leiden teacher Ludolph van Ceulen were engraved on what?

His tombstone in Leiden carried the digits after his death in 1610. The stone was eventually lost, and a restored version was put up in 2000.

Which astronomer's novel Contact imagines a creator's message hidden deep in pi's digits?

Carl Sagan has his heroine Ellie run a program that finds a circle drawn in zeros and ones far into pi written in base 11.

National Pie Day, an American dessert holiday separate from Pi Day, is celebrated in which month?

January 23 is National Pie Day because its founder, Colorado teacher Charlie Papazian, simply declared his own birthday a holiday in the 1970s.

Which gymnast from the gold-winning American team at Rio 2016 was born on Pi Day in 1997?

Simone Biles, a Pi Day baby from Columbus, Ohio, went on to have moves named after her on vault, balance beam and floor.

The Bible's description of a round basin in which king's temple implies that pi equals three?

Solomon's bronze basin, the Molten Sea, is described as ten cubits across and thirty cubits around, which would make pi exactly three.

In Yann Martel's novel Life of Pi, what is the name of the Bengal tiger sharing the lifeboat?

Richard Parker got his human name through a clerical error that swapped the tiger's name with that of the hunter who captured him.

Which ancient monument's base perimeter, divided by twice its height, comes strikingly close to pi?

The Great Pyramid is about 1,760 cubits around its base and 280 cubits tall, which gives 22/7, though most scholars doubt its builders meant to encode pi.

In which animated sitcom does a shopkeeper boast in court of reciting pi to 40,000 decimal places?

The Simpsons writers wanted Apu's boast to be right, so they asked a NASA researcher for the 40,000th digit of pi and were sent a printout: it is a one.

Which member of the Golden State Warriors' 2015 NBA title team was born on Pi Day in 1988?

Steph Curry was born in Akron, Ohio, and is widely regarded as the greatest shooter in basketball history.

Which gift-giving holiday, held a month after Valentine's Day, shares its date with Pi Day in Japan?

White Day began in Japan in 1978, and men who received Valentine's chocolate are expected to answer with a gift worth two to three times as much.

The formula T ≈ 2π√(L/g), built from length and gravity, gives the period of which simple device?

A pendulum's swing time depends on its length and on gravity but not on its weight, which is why pi is at work inside every grandfather clock.

Which children's maths book series includes 'The Dragon of Pi' and 'The First Round Table'?

Sir Cumference is a knight whose son, Radius, turns him into a dragon and back; the books by Cindy Neuschwander teach geometry through puns.

An infamous April Fools' hoax claimed which state's legislature had voted to change pi to exactly 3?

Alabama was only the setting: physicist Mark Boslough wrote the 1998 spoof to mock New Mexico lawmakers, yet people rang Alabama's legislature to protest.

Which Italian, who popularised Hindu-Arabic numerals in Europe, computed pi as 3.1418 around 1220?

Fibonacci reached 3.1418 with a polygon method of his own, and his Liber Abaci also gave Europe the famous number sequence that bears his name.

The Greek who first trapped pi between polygons was killed when Romans captured which Sicilian city?

Syracuse fell after a long siege, and a Roman soldier killed the mathematician despite orders that he was not to be harmed.

The formula πab, where a and b are the two semi-axes, gives the area enclosed by which curve?

An ellipse has this tidy area rule, yet its exact perimeter needs an elliptic integral, with no simple formula to match.

In which Sandra Bullock thriller does stumbling on a small pi symbol put the heroine's life in danger?

The Net has systems analyst Angela Bennett find the pi icon on a disk, and her identity is erased once the conspirators learn what she has seen.

In number theory, the function π(x) ignores circles and instead counts which integers up to x?

Primes up to x are tallied by π(x), so π(100) equals 25, because exactly a quarter of the first hundred integers are prime.

In maths notation, a capital pi written before a sequence of terms calls for which operation?

Multiplication of every term in the list is what capital pi demands, the partner of capital sigma, which tells you to add them all up instead.

The amateur mathematician behind America's notorious 1897 'pi bill' earned his living as what?

A physician by trade, he offered his home state free use of his 'new mathematical truth' in its schools, provided the legislature adopted it.

Which Dutch scientist, better known for a law of light refraction, pushed pi to 34 digits?

Willebrord Snellius, the Snell of Snell's law, had studied under Ludolph van Ceulen in Leiden, whose own polygon marathon reached 35 digits.

Which French fashion house has marketed a perfume named after the Greek letter pi?

Givenchy's π perfume is one of the examples writers reach for, alongside a feature film and Pi Day itself, to show how famous the number has become.

David Boll found pi's digits emerging from iteration counts near the 'neck' of which famous fractal?

The Mandelbrot set hides pi at its narrow 'neck': the closer a test point sits to it, the more steps it takes to escape, and those step counts trace out pi's digits.

Which software by Donald Knuth has version numbers that gain another digit of pi with each update?

TeX has crept towards pi one digit at a time since version 3, and Knuth says the final change, to be made after his death, will set the number to pi itself.

Which English savant, author of Born on a Blue Day, recited 22,514 digits of pi on Pi Day 2004?

Daniel Tammet set a European record with the recital, and scientists who later studied his memory found that he has synaesthesia.

Which French programmer, creator of FFmpeg and QEMU, once claimed the world record for digits of pi?

Fabrice Bellard set the 2009 record of nearly 2.7 trillion digits largely on a single desktop computer, and he had already found a faster formula for single digits of pi back in 1997.

Which Han dynasty polymath, inventor of an earthquake detector, took pi to be the square root of 10?

Zhang Heng's figure, about 3.162, runs slightly high; he derived it from his estimate of how much of a cube an inscribed ball fills.

Which co-author of The Communist Manifesto died in London on Pi Day in 1883?

Karl Marx died a stateless person at 64 and was buried three days later in Highgate Cemetery, in a plot reserved for agnostics and atheists.