It's the only holiday to honor a number: Pi Day, on 3-14, the beginning digits of the infinite, nonrepeating decimal expansion of $\pi$ = 3.1415926... As the ratio of a circle's circumference to its diameter, $\pi$ is irrational and transcendental--qualities sure to bring a twinkle to any mathematician's eyes. How are people celebrating Pi Day?

- Let's start with some music! Here's Noam Elkies' composition, Steganographic Étude #1, based on the first 244 digits of $\pi$, with an explanation.
- Who came up with Pi Day? Learn about the day's history.
- The 2021 Global Online Celebration of the International Day of Mathematics (IDM) is a project led by the International Mathematical Union. All talks, available in English, French and Spanish, will be streamed completely free and without any need to sign up.
- Take Math to Mars and Beyond with NASA's Pi Day Challenge.
- The Exploratorium in San Francisco hosts events every year.
- Check out these fun activities.
- National Council of Teachers of Math (NCTM) "Pi Day on Pinterest".
- Math Goodies offers lesson plans.
- College and university math departments such as University of Waterloo, Edinboro University, and St. Bonaventure University have fun on Pi Day.
- See Happy Pi Day video on YouTube. Dr Eugenia Cheng, from the University of Sheffield, explains what Pi is, what it's useful for, and demonstrates a trick to remembering it.
- Read more about Pi Day on AMS Blogs:
*The Pi Day Link Roundup of the Century*, by Evelyn Lamb,*Pi Day and Other Math Holidays*, by Maya Sharma, and*The Ubiquity of Pi Day: It’s Not Just for Math Geeks*, by Edray Goins. - Search Twitter for hashtag #PiDay to see lots more Pi Day celebrations around the world.

**If your math department celebrates Pi Day let us know!**

Email us at AMS Outreach

*Photo courtesy of Kay Sweet*: the first 13 digits of Pi (last displayed digit rounded).