March 14, celebrated as Pi Day as the first three digits of the number are 3.14, was being marked in New York with a pi-themed scavenger hunt at the Museum of Mathematics, the New York Daily News reported Thursday.
Matthew Plummer, a former math teacher at Boston's Hanover High School, was inviting people to take the "Pie Day Challenge" with math puzzles on his website, pidaychallenge.com.
Meanwhile, the number, which is used to calculate the circumference of a circle, is the subject of a Pi Day Pie Baking Contest hosted by website Serious Eats, which is taking submissions of recipes and pictures of the finished product.
Students at the California Institute of Technology kicked off Pi Day at 1:59 a.m. Thursday with 160 pies -- 26 each of five kinds -- to mark pi to nine digits, 3.14159265, the Los Angeles Times reported Thursday.
"It's a celebration of nerdiness," said Christopher Perez, president of Caltech's math club. "Pi literally shows up everywhere -- in science, in math and nature. A circle is such a fundamental concept."