Fibonacci series

A Fibonacci series is a series of numbers in which any number (from the third onward) is equal to the sum of the two previous numbers.

All that is necessary is to take two starting numbers. Adding them gives a third, then the second + the third gives the fourth and so on. In any Fibonacci series the ratio of the last two numbers (the larger/the smaller) tends to the value 1.61803..., the golden number.