In this recipe, we will calculate fibonacci numbers by writing a simple recursive function. Fibonacci numbers are the numbers appearing in the fibonacci sequence.

Fibonacci numbers are calculated as follows:

*F _{n} = F_{n-1} + F_{n-2}*

We need to provide the first two seed fibonacci numbers in the sequence so that we can calculate the next set of fibonacci numbers. We will seed the sequence with `0` and `1`. Our sequence will look like this:

*0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144 ....*

We will start indexing with `0`. Hence, the 0^{th} fibonacci number is `0`, 1^{st} fibonacci number is `1`, .. 5^{th} fibonacci number is `5` ... and so on.