## 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.

## 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."

## 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.

## 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.

## 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.

## 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.

## "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!

## 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!

## 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?

## 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.