Capturing the rabbit formula in the form of a C function, you have the following:

#include/* Define rabbits function */ int rabbits (int n) { if (n == 0 || n == 1) return 1; else return rabbits (n - 1) + rabbits (n - 2); } /* Test rabbits function */ main ( ) { printf ("At the end of month 1, there is %i.\n", rabbits (1)); printf ("At the end of month 10, there are %i.\n", rabbits (10)); printf ("At the end of month 20, there are %i.\n", rabbits (20)); } --- Result --- At the end of month 1, there is 1. At the end of month 10, there are 89. At the end of month 20, there are 10946.