/** @return Binomial coefficients with recursion, i.e. n choose k, C(n,k) or nCk. */
int CombinatorialRec(int n, int k)
	/* We could do: 
			return factorial(n)/(factorial(n-k)*factorial(k));
		But prefer the recursive approach instead, because it's not so prone
		to numerical overflow. This approach uses the idea of the Pascal triangle. */

	if (k <= 0 || k >= n)
		return 1;
		return CombinatorialRec(n-1,k-1) + CombinatorialRec(n-1,k);