Fibonacci number

The Fibonacci numbers are numbers generated from the following formula:


 * F1 = 1
 * F2 = 1
 * Fn = Fn-1 + Fn-2

As the terms get larger, the ratio between two consecutive terms approaches the golden ratio, about 1.618.

Examples
The first twenty terms of the sequence are:

1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181, 6765