Pi Day: An Infinite Number of Ways to Celebrate

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On Friday, math enthusiasts celebrate pi, the infinite number representing the relationship between a circle's circumference and its diameter. Represented by the Greek letter pi, the number is usually shortened to 3.14, so festivities take place on March 14 or 3/14.

Across the country, math aficionados trade pi recipes, hold pizza parties, and recite as many digits of the never-ending number as they can remember. (Listen to a recitation by Mark Umile, North American record-holder for memorizing pi.)

Physicist Ron Hipschman talks with host Ira Flatow about the all-day pi celebration taking place at the Exploratorium in San Francisco.

Pi Day Celebrates a Mysterious Number

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Pie

Math lovers honor Pi Day by eating pie, of course. NPR hide caption

itoggle caption NPR

A lot of people are excited about the power of pi. But not everyone knows it has an official celebration — Pi Day, on the fourteenth day of the third month, 3.14. Those are the first three digits of pi, that transcendental number, the icon with the digits after the decimal point that go on forever.

Strictly speaking, pi represents the constant ratio of a circle's diameter to its circumference. There is no pattern to pi. But it's a cool number with real-life applications. Today, as Dan Hellerich of PiDay.org reports, numbers geeks all over the world bake pies, write "pi-kus" and recite pi to as many decimal points as possible. "I know 15," he says. "Some people know 10 times that, but you really only need about 10 to do accurate math in geometry or physics."

Pi has been around a long time. A man named William Jones identified the magical number in the 1700s. But the dedication of day to the love of pi is a more recent development. And — as another pi super-fan says — unless our calendars get a major adjustment, no other date can hope for 3.14's level of distinction.

"You can't find a 'square root of two' day," the super-fan says. The square root of two is roughly 1.44. "That would be January 44. And E? That would be February 71. You can't celebrate that."

On our blog, a challenge: Write your own "pi-ku".

Happy Pi Day from the Pi Guy

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41 Dozen Numbers of Pi

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Math lovers celebrate March 14 (or "3-14") as Pi Day.

The Greek letter pi represents the mathematical constant that equals a circle's circumference divided by its diameter. The world's most famous irrational number is usually shortened to 3.14 — but not for Marc Umile.

In January, the 40-year-old from Upper Darby, Pa., became the North American record-holder for memorizing pi: He made it to the 12,887th digit.

Umile says he has always been fascinated with human memory.

"For anybody who wants to know how good their memory is, pi is the ultimate test of finding that out," Umile tells Robert Siegel.

A love of music helped Umile memorize the digits of pi. He says he separated the numbers into clusters of 2, 4 and 6, and he also recorded himself reciting pi, and listened to it repeatedly.

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