Saturday, August 22, 2009

Remembering the digits of Pi

My favourite subjects at school were science and mathematics. I was fascinated by the number "Pi" and how the numbers after the decimal point went on for ever. Pi was my first transcendental number.

Pi is the ratio of the circumference of a circle to its diameter.

At first I was taught that Pi was approximately equal to 22/7. This is only accurate to two decimal places (3.1428571...)

I learnt a better approximation was 355/113 which was interesting because it has a pattern of repeated odd numbers 113355, split into two (113 and 355) then made into a fraction. It is accurate to sixdecimal places: 3.1415929.

For some reason I memorised Pi to 12 places (3.141592653589) using rote learning. I remembered the sounds and rhythms of saying these letters out loud.

But how can we memorise the numbers using a mnemonic?

A traditional way to remind yourself of the decimals is to use phrases containing word-length mnemonics, where the number of letters in each word corresponds to a digit.

Pi to 6 decimal places:

How I wish I could calculate Pi

This gives Pi as 3.141592

Pi to 14 decimal places:

How I like a drink,
alcoholic of course,
after the heavy lectures involving
quantum mechanics

This gives Pi as 3.14159265358979

And here's a rhyme to 20 decimal places of Pi:

Now, I wish I could recollect pi.
'Eureka,' cried the great inventor.
Christmas Pudding, Christmas Pie,
Is the problem's very centre.

This gives Pi as 3.14159265358979323846

And to 31 decimal places:

Sir, I bear a rhyme excelling
In mystic force, and magic spelling
Celestial sprites elucidate
All my own striving can't relate
Or locate they who can cogitate
And so finally terminate. Finis.

This gives Pi as 3.1415926535897932384626433832795

This useful method of remembering Pi only works up to thirty-one decimal places, unfortunately, because the thirty-second number after the decimal point is 0.

Memorising large sequences of the decimal value of Pi appears to be part of memory competitions. The number sequence is not random, but it can't be predicted. Read more about Pi at Wikipedia

Mathematics is the subject I have studied the most in my life. I have a Bachelor of Science majoring in Pure Mathematics and Computer Science, but since leaving university I have developed interests in many other areas of life.

I highly recommend the film Pi, the 1998 American psychological thriller directed by Darren Aronofsky.

Verses from "I before e (except after c) - old school ways to remember stuff" by Judy Parkinson (c) 2007


  1. Honestly I really dont like Math subject but it not means that I dont want Pi symbol.

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  2. Thank you for sharing. I memorized 512 digits of Pi easily by this two new memorization techniques, it's very unique and works for most people -->