Episode three of Five Numbers, the BBC radio series presented by Simon Singh.

Divide any number in the Fibonacci sequence by the one before it, for example 55/34, or 21/13, and the answer is always close to 1.61803. This is known as the Golden Ratio, and hence Fibonacci's Sequence is also called the Golden Sequence. Unlikely though it might seem, this series of numbers is the common factor linking rabbits, cauliflowers and snails.