March 14 is “Pi-Day” (3.14, get it?), a beloved holiday for math geeks nationwide. If you’re a student or teacher, you’ll probably be celebrating this fun day in school — hopefully with some apple pie, or pizza pie, or both. But before you take out your paper plates and dust off your geometry puns, here are 3 + 1 + 4 fun facts about this namesake irrational number:

**1. Pi is a ratio; as such, it never changes.** It is defined as the ratio of a circle’s circumference to its diameter:

**𝛑 = circumference / diameter**.

**2. Though pi is irrational **(meaning that it can’t be expressed by a simple fraction, and the decimal points go on forever without repeating)**, it is often represented by a rational number**: most often 3.14 or 22/7

**3. Some international math fanatics choose to celebrate Pi Day on July 22 instead of March 14.** The reason? Outside of the US, most countries write dates as day / month. In this style, July 22 is written as 22/7 — or the fractional representation of pi.

**4. The discovery of the neverending number has been credited to Archimedes of Syracuse**, who lived in the third century BC. He identified pi while determining how to accurately calculate the area of a circle based on the length of its radius. Several approximations of pi were used prior to the one we know today, dating back nearly 4000 years. In fact, there are records of the Ancient Egyptians expressing the area of a circle as 3.1605(radius) and the Ancient Babylonians as 3.125(radius) as early as 1900- 1600 BC.

**5. Understanding 𝛑 takes a village.** Mathematicians attempting to define pi have build upon one another’s theories since the earliest days of geometry. From scholars in ancient China and the Middle East, to those in 14th- 15th century India and 17th century Japan and Europe, to modern-day computer scientists collaborating internationally, it has been a real team effort to build our universal knowledge of pi.

**6. The symbol that we now use for pi — 𝛑**** — was actually made popular by a math teacher!** Historians have credited modern adoption of the symbol to teacher William Jones, who printed it in a book of notes called *Synopsis Palmariorum Matheseos, or A New Introduction to the Mathematics* in 1706 (talk about an intimidating textbook title). He held the philosophical belief (shared by modern day mathematicians) that pi can *only* be expressed by a symbol in formulas, as it is impossible to define its numerical value.

**7. We will never know the final digit of pi — but we can get to digit #****22,459,157,718,361!** In November 2016, particle physicist Peter Trueb used a computer (which had been running 24-hours of calculations for 105 days) to reach a world-record in the number of digits of pi uncovered. The previous record, set in 2013, was 9 *trillion* fewer digits.

**8. Akira Haraguchi of Japan has memorized and recited more than 100,000 known digits of pi.** The then-60 year old pulled off this impressive feat in 2006, blowing other records out of the water (though his accomplishment has not been officially recognized by Guinness). He considers the memorization of these digits, which took him more than 16 hours to recite aloud, a spiritual pursuit.

**Q: Why shouldn’t you talk to Pi?**

**A: Because once he starts, he’ll never stop!**

Ultimately, Pi Day celebrates more than just a symbol for use in geometry class. The significance of pi cannot be understated; anywhere a circle goes — think architecture, vehicular design, patterns in the natural world, bell curves, even the human eye — there goes pi. Pi is used to measure probability and statistics, and has endless real-world applications in the fields of science and medicine. So as you dig into your pi day celebrations, remember to thank that little symbol for holding up so much of our world.