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21 Fascinating Facts Behind the Mystery of Pi

Find out why this ancient mathematical constant gets an annual celebration—one that's growing every year!

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The mystery of pi

How many numbers can you name in pi? If you know these facts, chances are you can probably name a lot. If you can’t name that many, read on to learn about the mysteries of the number mathematicians named “pi.” And if you like these pi facts, check out some more interesting facts about basically everything.

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People have been using pi for thousands of years

Pi (the Greek letter π, pronounced like the word “pie”) is the ratio of the circumference of any circle to the diameter of that circle, explains math instructor Steven Bogart in Scientific American. It equals roughly 3.14. No matter what size a circle is, the circumference will always be 3.14 times bigger than the diameter. Over 4,000 years ago, the ancient Egyptians and Babylonians had figured out this constant and were using it to make calculations. In the 18th century, mathematicians gave the number the name “pi.”

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We celebrate pi on March 14

Back in 1988, Larry Shaw of San Francisco’s Exploratorium science museum started observing March 14—get it? 3/14!—which also happens to be Albert Einstein’s birthday, as Pi Day. By 2009, the celebration had grown so big that Congress passed a resolution to make the designation official. The resolution states: “The House of Representatives supports the designation of a ‘Pi Day’ and its celebration around the world … and encourages schools and educators to observe the day with appropriate activities that teach students about Pi and engage them about the study of mathematics.” In another stamp of approval, in 2010, Pi Day got its own Google Doodle. Here are 14 ways to celebrate Pi Day or, if March 14th is still far off, to celebrate your acquisition of such great pi facts! Including but not limited to the actual consumption of pie.

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Pi is a never-ending number

Pi is an irrational number. It can’t be expressed as a fraction; it doesn’t end with a repeating pattern (like the decimal expression of 1/3, 0.33333…, in which the threes repeat forever), or terminate after a certain number of decimal places (like 3/4, or .75). It just keeps going, going, and going. So far, pi has been calculated to over 22 trillion digits. It took a computer with 24 hard drives, working nonstop for 105 days, to make that calculation. These cool math tricks (which you will wish you had always known) are an excellent addition to all your new pi facts.

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The digits of pi after the decimal point are random

Here’s a mind twisting pi fact: the trillions of digits of pi that have been calculated continue without any discernible pattern. Mathematicians have been looking for those patterns for centuries, but as far back as 1768, a self-taught Swiss-German mathematician and astronomer named Johann Lambert proved that pi is irrational.

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More pi isn’t necessarily better

While we know pi to more than a trillion places, we really don’t need them. Scientists can determine the spherical volume of the entire universe using just 39 places past the decimal, according to piday.org. NASA’s Jet Propulsion Laboratory only uses pi up to 15 decimal places for its robotic space and earth science missions. “For JPL’s highest accuracy calculations, which are for interplanetary navigation, we use 3.141592653589793,” explains engineer Marc Rayman. “There are no physically realistic calculations scientists ever perform” that would require more decimal points than that. Test your math skills by seeing if you can pass this elementary school math test.

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“Pi” is much shorter than the number’s previous name

The number’s connection with the Greek letter π is actually pretty recent, considering that people have known about the quantity since the time of the ancient Babylonians. A British mathematician named William Jones was the first person to call the quantity π, in 1706. People theorize that he chose pi because it represents the Greek letter P, and pi can find the perimeter of a circle. People have found math books from before 1706 that refer to the number as a lengthy Latin phrase that translates to “the quantity which, when the diameter is multiplied by it, yields the circumference.” Anyone who talks about math for a living, as well as anyone who likes finding excuses to eat pie, owes this Jones fellow one!

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State lawmakers once tried to round up pi to 3.2

If we don’t need all those decimal places in pi, wouldn’t it be easier to just call it 3.2? In 1897, an Indiana doctor decided that the world should go ahead and use 3.2 for any calculations requiring pi. Dr. Edwin Goodwin proposed a bill in the state legislature. He even copyrighted this idea and planned to charge royalty fees for anyone who used it—except for those in the state of Indiana. After some debate, the state senate realized that the idea of using a law to change a mathematical constant was a silly one, and the law failed to pass. If you think legislating pi is silly, check out the dumbest law in every state—and they’re all for real!

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Someone has memorized 70,000 decimal places of pi

The Guinness Book of World Records recognizes Rajveer Meena as the champion memorizer of digits of pi. On March 21, 2015, at VIT University in Vellore, India, Meena recited pi to 70,000 places past the decimal point. A 21-year-old student at the time, Meena proved his powers of memory by reeling off the numbers while wearing a blindfold. It took him more than nine hours to do it. Can you guess the highest number anyone has ever counted to?

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You can borrow expert memorizers’ techniques

How in the world does someone memorize a string of 70,000 random numbers? Most record-holders (or just interested hobbyists) use an association technique. They bunch smaller groups of numbers together and memorize those: 14, then 15, then 92, then 65, and so on. Or they may look at each set of nine digits as a telephone number and memorize them that way. Another strategy is to match each digit or small groups to a word, then make a story out of those words. Yet another method is spatial visualization, in which you picture a familiar place, then assign numbers to different spots in that place. To recall them, you mentally walk through the space and see the numbers as you go. If you’re looking for other ways to train your memory, here are quick brain exercises you can do right now.

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Pi is a record-setter in more ways than one

Aside from Rajveer Meena’s achievement, other Guinness World Records have been awarded to pi-themed accomplishments. In 2014, 589 people at a grammar school in Germany formed the largest human pi symbol. And in 2017, 520 teachers and students in Todi, Italy, formed the longest human representation of pi digits. The city’s mayor held up a sign bearing the number 3, and then each person after him stood in for a digit of pi after the decimal place.

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Pi has many real-world uses

It’s not all fun and games and feats of memory: Scientists use pi every day to make important calculations, such as determining the volume of a sphere, the area of a circle, and the volume of a cylinder. “Those relationships form the basis for how stiff a structure is, how it will vibrate, and understanding how a design might fail,” says Charles Dandino, an engineer at the Jet Propulsion Lab. “In my career, pi has allowed me to calculate the size of a shield needed to enter the atmosphere of Venus and the size of a parachute that could safely land the Curiosity rover on the surface of Mars,” says another JPL engineer, Anita Sengupta. Another handy tool that makes use of pi? The GPS system in your car and smartphone use it to calculate specific locations on Earth.

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Do a magic trick to calculate pi

To try this easy activity known as Buffon’s Needles, you need a large sheet of paper, at least 30 toothpicks, a ruler, and a pen. Using a toothpick to determine the distance between them, draw a series of parallel lines on your paper. Then throw the toothpicks onto the paper at random.

Next, take away any toothpicks that are only partially on the paper, or that didn’t land on the paper at all. Count how many are left on the paper. Also, count how many cross a line.

Divide the total number of toothpicks by the line-crossing toothpicks. Now multiply by two, and you should get pi! Check out these other brain-boosters you can do with your kids.

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Pi is a movie star

Pi has made several significant appearances in pop culture. Most notably, there is an entire film about it, called Pi: Finding Faith in Chaos. The 1998 film, which won an Independent Spirit Award for screenwriter Darren Aronofsky, is admittedly a bit of a downer, as it follows a tormented mathematician trying (and failing) to work out the secrets of the universe. In the Sandra Bullock thriller The Net, clicking on a pi symbol is what sends Bullock’s character into the confidential government files, and in Alfred Hitchcock’s Torn Curtain, the pi symbol is the code that represents the escape network. It’s even vanquished TV villains; in a Star Trek episode, Spock outsmarts an evil computer by challenging it to calculate the final digit of pi.

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A pi-themed crop circle left scientists scratching their heads

In 2008, a 150-diameter crop circle suddenly appeared by Barbury Castle, near the English village of Wroughton. Researchers and conspiracy theorists puzzled over its origin and meaning, and an astrophysicist eventually figured out that the image was a code representing the first ten digits of pi. Learn about some of the most baffling unsolved mysteries about the universe.

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Pi makes people laugh

As it’s a monosyllabic word that also happens to sound exactly like a yummy dessert, there’s no shortage of jokes and puns to be made about pi. “What kind of reptile do math teachers keep as pets?” “Pi-thons!” “Why should you never start a conversation with pi?” “Because it goes on forever!” A comedian named John Evans even used a pi-themed joke in one of his routines: “What do you get if you divide the circumference of a jack-o’-lantern by its diameter? Pumpkin pi!” And the best part is, telling pi-themed jokes makes you sound smart while you’re making people laugh. Who says math can’t be fun?! If pi facts aren’t quite your thing, here are our favorite jokes about pi, and math in general, to celebrate Pi Day.

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Pi can go the distance

You can see what pi to one million decimal places looks like, here, at piday.org (keep scrolling!). Another way to visualize this super-long number? If you printed out pi to a billion decimal values, in 12-point font, you’d need a piece of paper that stretched halfway across the United States, from Kansas to New York City.

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Celebrate Pi Day with a 5K

Besides being a nice rhyme, a 5K is pretty close to 3.14 miles in length (it’s 3.10686 miles, to be exact). So schools and communities around the country host 3.14 mile runs on or near Pi Day every year. We found them in Newark, Delaware; Monroe, Connecticut; South Bend, Indiana; Green Bay, Wisconsin; and Tempe, Arizona. Find out which math lessons you’ll actually use in real life.

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Better yet, celebrate pi with pie

It’s already a Pi Day tradition: pie in all its glory! Pizza pie, pot pie, shepherd’s pie, and of course, dessert pie. Just make sure it’s round! Prefer a no-bake pie? Skip the oven with these 30 no-bake pie recipes you’ll want to make tonight.

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Pi’s double has some fans, too

It would seem that every massively popular thing inevitably has some detractors, too, and pi is no exception. A growing number of math lovers have begun to argue that a number called “tau,” which is two times pi, deserves at least as prominent a place in the math world as pi. Tau, whose approximate value is 6.28, is the relationship between the circumference of a circle and its radius, while pi relates the circumference to the diameter. Since the radius is a more useful mathematical quantity, many believe that tau is a more intuitive mathematic value than pi.

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Pi inspires poetry

You can also observe Pi Day with a poem… or a “piem”! Pilish unites math enthusiasts and word nerds. To compose in it, you must use words in which the number of letters corresponds, in order, to the numbers in pi’s sequence. So since pi = 3.14159, your poem must start with a three-letter word, then a 1-letter word, then a 4-letter word, another single letter, and so on: “Aha, I said, a fancy alligator …” Now, check out our 12 trickiest math riddles.

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And Pi Day inspires awesome Pi Day deals

All across the country, local and national stores are celebrating Pi Day with sweet (and savory!) deals. Whole Foods, for example, is giving a $3.14 discount on all pies. Or get a pizza pie from Blaze Pizza or Papa John’s Pizza at a special Pi Day price. Celebrate Pi Day and share all these amazingly cool pi facts. You can find these deals and more at piday.org.