Fibonacci sequence

The Fibonacci Sequence is a sequence that appears often in nature. It is usually defined with:


 * $$a_0$$ = 0
 * $$a_1$$ = 1
 * $$a_i = a_{i-1} + a_{i-2}$$ for all $$i \geq 2$$.

The first few terms are: 0, 1, 1, 2, 3, 5, 8, 13, 21...