Pi In The Face

In the "Notebook" section of the March 18, 1996, issue of The Scientist [page 30], there is a short piece about someone who has constructed a mnemonic device to remember 167 digits of the number p. The first sentence of the piece wrongly states that 22 over 7 "is represented by p." p is an irrational number, which means that it cannot be written as the ratio of two whole numbers. 22/7 is rational because it is the ratio of two whole numbers. Any rational number can be written either as a decima

Apr 29, 1996
Allyn Jackson

In the "Notebook" section of the March 18, 1996, issue of The Scientist [page 30], there is a short piece about someone who has constructed a mnemonic device to remember 167 digits of the number p. The first sentence of the piece wrongly states that 22 over 7 "is represented by p." p is an irrational number, which means that it cannot be written as the ratio of two whole numbers. 22/7 is rational because it is the ratio of two whole numbers. Any rational number can be written either as a decimal number with finitely many digits (for example, 1/8 = .125), or as a decimal number made up of an infinite repetition of a finite string of digits (for example, 125/999 = .125125125...).

The decimal expansions of irrational numbers like p are infinitely long and nonrepeating. What all this means is that no matter how many digits of p you memorize, there will always be more.

A mnemonic for remembering 167 digits is cute, but not that impressive. According to a New York Times profile of the mathematician John H. Conway of Princeton University, he has memorized p out to 1,000 digits.

Allyn Jackson
American Mathematical Society
P.O. Box 6248
Providence, R.I. 02940-6248
E-mail: axj@math.ams.org