March 14 (3/14) is Pi Day and July 22 (22/7 in the European date style) is Pi Approximation Day. In mathematics a common shortened figure for pi is 3.14 while the most well-known “approximate pi” is 22 divided by 7 (3.1428571428571428). These two celebrations of the most famous irrational number on dates related to that number are part of the folklore of students and scholars in fields such as mathematics, the sciences, engineering, and architecture. The first public celebration of Pi Day was organized by physicist Larry Shaw at the Exploratorium museum in San Francisco in 1988. The day was recognized by the U.S. House of Representatives in 2009. March 14 is also Albert Einstein’s birthday, so celebrations of pi and Einstein are sometimes combined; for example, Princeton University holds an Einstein look-alike contest along with events celebrating pi.

The beginnings of celebrations of pi gave rise to discussions concerning which calendar day is most appropriate, because 22/7 is a more precise approximation of pi than 3.14. It is commonly used in science, engineering, and architecture when a more precise figure is not required. It has a venerable history, as Archimedes (ca. 287-212 BC) wrote the first known proof that 22/7 is greater than pi. But pi written as 3.14 is more widely known by math students and the general public. Each day has its proponents, resulting in the two commemorative days, both celebrated internationally. Pi Approximation Day may have begun at Chalmers University, Gothenburg, Sweden in 1995.[1] (If there was an earlier celebration, I would be interested to hear about it.)

Both Pi Day and Pi Approximation Day may be celebrated with mock or serious theoretical discussions related to pi; mathematical games; the consumption of circular foods, especially pie (including pizza pie); pie baking; pie tasting contests; pie eating contests; and pie throwing. In the United States it has become customary to walk or run 3.14 miles, perhaps to work off some of that pie! In addition to pie, celebrants of Pi Approximation Day may enjoy a treat that is an “approximation of pie” such as blueberry cobbler or peach crumble. When it comes to making and eating pies, Pi Approximation Day does have a gastronomical advantage in much of the northern hemisphere, with a greater abundance of fresh produce to make pie with.

Another way to celebrate pi is to learn and recite the digits as far as memory allows. At pi events, competitions may be held to see who can recite pi to the most decimal places. Mathematical folklore includes mnemonic devices for pi: phrases, rhymes, songs, and stories with the number of letters in each word representing the value of a digit (punctuation is not counted). In rare cases when a word used has more than nine letters, the word represents two digits. Such works are sometimes recited at pi events, as well as used as tools for memorization. Some popular examples are “May I draw a circle?” (3.1416, an approximate pi), “May I have a large container of coffee?” (3.1415926), and “May I have a large container of coffee, sugar and cream?” (3.1415926535). Rhymes are a common tool for memorizing long strings of digits of pi. For example:

How I wish I could recollect of circle round

The exact relation Archimede unwound.

(3.1415926535897 This old favorite has many variations relying on nine-letter, rather than ten-letter, spellings of “Archimedes.”)

Now I will a rhyme construct

By chosen words the young instruct.

Cunningly devised endeavour

Con it and remember ever.

Widths in circles here you see

Sketched out in strange obscurity.

(3.141592653589793238462643383279 Note that the British spelling of endeavour is required in this one; to stand for the number 9.)

The term for this type of encoded writing is “pilish.” Creating and memorizing works in pilish is a pastime, rather than a necessity. The mnemonics are enjoyed by students of math and participants in memorization contests and are created by students, academics, and other fans of pi. Mathematician Antreas P. Hatzipolakis’s interest in folklore led him to compile a large collection of these in many languages, “Pi Philology,” 1998. (The site includes an autobiographical “FAQ.”)

Many pi mnemonic devices do not have known authors. To my knowledge, the examples above are anonymous. But there are also works in pilish that have been passed along with the authors’ names and a few have been published. Some are of such a length that they cease to have practical value for memorization, but are entertaining to read. The longest pi poems and stories to date are by the mathematician and author of several works of constrained writing, Michael Keith. His work of prose and poetry, *Not A Wake: a Dream Embodying π’s Digits Fully for 10000 Decimals (2010)*, does exactly what the title says, with the title providing the first sequence of digits.[2] Participants in pi recitation contests are invited to devise their own mnemonics. New favorites may be passed on and recited in future celebrations of pi.

**Notes**

- “Pi Approximation Day,” by Martin Rebas. This article describes the celebrations of approximate pi in the 1990s at Chalmers University, Gothenburg, Sweden. Martin Rebas attended these annual events from 1995 through 1997.
- As of March 2014, Keith’s
*Not A Wake…*was credited as the longest work in pilish and I cannot find any evidence that it has been surpassed.