Stirling(n,r)

Partition of n distinct objects in r non-empty groups

This function calculates the total no. of partitions of n distinct object in r groups such that each group as at least one element. This number is also called 'Stirling numbers of the second kind'.
Input:
n -no. of objects
r - no. of partitions
output: no. of permutations
Ex>> Stirling(10,3)=9330;