Book of the week

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Did you know that if you measure the circumference of your head in inches and divide by p, then round to the nearest eighth, you get your hat size? Did you know that the millionth digit of p is 1, or that the 360th digit and the two on each side of it read "360"?

I learned these marvellous pieces of information from a new book, The Joy of p (Allen Lane, pounds 12.99), by David Blatner. The major part of this book is a history of man's quest to achieve ever more accurate approximations to the ration between the circumference and diameter of a circle. It is the story of geniuses and obsessives, from such great mathematicians as Newton and Euler, both of whom made significant contributions to the theory of p (indeed it was Euler who was the first to call it by the name of the Greek letter for p), to modern-day p-hunters such as the Chudnovsky brothers, who calculated 8 billion digits of p in 1996, and Kanada and Takahashi who extended the record to over 51 billion digits this year.

The book is beautifully designed to include the first million digits. The perfect Christmas gift for anyone fascinated by mathematics.