Calculate the (binomial coeficient)[https://mathworld.wolfram.com/BinomialCoefficient.html], representing the number of ways to choose an (unordered) subset of k elements from a fixed set of n elements. It can be calculated by the expression:
B(N,K) = N! / K! * (N-K)!
For example: B(4,2) = 6 B(5,3) = 10