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Mnemonic Techniques for Numbers

We use numbers every day of our lives. From telephone numbers and social security numbers, to airline flight numbers and order numbers. For some of these numbers it is very useful to be able to memorise them. If they are just two or three digits this is not usually too difficult, but a telephone number may be as many as twelve or more. Here are some mnemonic devices for remembering pi, and for telephone numbers.

Mnemonics for the number Pi

There once was a fellow from Greece,
Who forgot pi's last decimal piece.
So he used electronics
To collect pi mnemonics...
Now he's hooked, and there is no release.

                Michael P. Masterson-Gibbons

Pi is the ratio between a circle's circumference and its diameter. When expressed decimally it extends to infinity as a series of apparently random digits. It is useful to scientists to know approximately the value of pi, perhaps to two or three decimal places. If it is required to a greater accuracy, then generally calculators and computers can be used.

You may question, then, the usefulness of mnemonics for memorising pi to many more digits. It can only be for the challenge itself. One gentleman, Hiroyuki Goto, recited no less than 42,000 digits of pi from memory in 1995. This record feat took him about nine hours to complete.

Pi = 3.1415926535897932384626433832795028841971...

The most common type of mnemonic is the word-length mnemonic in which the number of letters in each word corresponds to a digit. This simple one gives pi to seven decimal places:

How I wish I could calculate pi.

This longer one, giving fifteen decimal places of pi, is popular with students:

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

There is the little rhyme to aid the memorisation of twenty-one digits of pi:

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

And if you feel the need for a device for remembering thirty-one decimal places of pi, try this rhyme:

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.

There is a problem with this type of mnemonic that does not affect the above examples. It is the question of how to represent the digit zero. Fortunately a zero does not occur in pi until the thirty-second place. Several people have come up with ingenious methods of overcoming this, most commonly using a ten-letter word to represent zero. In other cases a certain piece of punctuation indicates a naught.

There are many stories and poems crafted in this way, and at least one encoding over 700 digits of pi.

Telephone Number Mnemonics

American visitors to will be familiar with an ingenious method of making telephone numbers more memorable. In the USA many companies advertise their telephone numbers with words. For example "Call 1800-CAT-HELP" might be the advertising slogan for a feline rescue centre. This is much easier to remember than "Call 1800-228-4357".

To aid this system, the buttons on telephones are marked with letters too, as shown on the right. This method has been used in Britain too, although it is now far less popular. Nevertheless many British telephones are marked with letters too.

A more usual technique used by British companies for making telephone numbers memorable is to have a numerically very simple number such as 0800 100 200 or 0845 45 45 45.

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