March 14 (3/14) is Pi Day, a celebration of the ratio of a circle’s circumference to its diameter — one of the most beautiful and confounding numbers in mathematics. It’s technically written as 3.14159, or 3.14 for short, but Pi is an “irrational and transcendental number” whose decimals “continue infinitely without repetition or pattern,” according to PiDay.org, the holiday’s official website. But just like the hordes of young people who flocked to get married on 12/12/12, we can’t resist the opportunity to celebrate a fortuitous coincidence on our calendars. Here’s our favorite quirky celebrations for Pi Day 2013.

(MORE: Pi Day By The Numbers)

• In the past, MIT has posted its acceptance letters to high school seniors on Pi Day.

• Attention, Chicago residents: First Slice Pie Café will be giving out free slices of pizza today at 3:14 pm. For readers in the Southeast, pizzas cost $3.14 at…