gistfile1.txt

table = {}

def f(n, k):
    if (n, k) not in table: #compute if not yet visited
        if n == 1:
            table[n,k] = k-1
        if n == 2:
            table[n,k] = k*(k-1)
        if n >= 3:
            table[n,k] = (k-1)*f(n-1, k) + (k-1)*f(n-2, k)
    return table[n,k]