This function is used to calculate the number of k-combinations from a given set with n elements, denoted by:
Please note that a combination is different from a permutation in which the combination is a set of elements regardless of the internal order, while the internal order in a permutation is significant. For example, in the 3 elements of "a, b, c", "ab" and "ba" are considered the same combination but two different permutations.
double Combine(int n, int k)
Return the number of k-combinations from a given set with n elements
combine(4, 2) = ; // returns 6
Combine(8, 2) = ; // returns 28
Combina, Permut, Permutationa