**n = n(-1) + n(-2), where the n(-1) means “the last number before n in the series” and n(-2) refers to “the second last one before n in the series.”**

In computer programming, Fibonacci numbers give a model for designing recursive programming algorithms where the time for any routine is the time within the routine itself, plus the time for the recursive calls.

The Fibonacci numbers were originally defined by the Italian mathematician Fibonacci, also known as Leonardo da Pisa, in the 13th century to model the growth of rabbit populations.