Celebrating Pi Day

Updated 12:03 PM ET, Thu March 14, 2013
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March 14 is Pi Day, 3-14! Daniel Tammet painted this picture of how he sees the first 20 digits of pi. He set the European record for memorizing and reciting digits in 2004. Courtesy Daniel Tammet
The Exploratorium in San Francisco hosts an annual parade on Pi Day, where fans of the number make handmade number signs and march in order of pi's digits (3.14 ... ). Exploratorium
The Exploratorium is installing this "pi shrine" on the sidewalk in front of its new location in San Francisco on Pi Day 2013. Exploratorium
Pi is the ratio of circumference to diameter of a circle. You may have learned this in geometry class. It is approximately equal to 3.14.
iReporter Zeynep Rice made this pie. The main filling is derived from a deep dish apple pie recipe, and she added pears. Courtesy Zeynep Rice
CNN's Eatocracy blog has lots of pie recipes for you to try. Pi Day is also Albert Einstein's birthday. Elizabeth Landau/CNN