session 9 ?

def factorial(n):
    ret = 1
    for x in range(2,n+1):
        ret = ret * x
    return ret

def factorial_rec(n):
    if n == 1:
        return 1
    return n * factorial_rec(n-1)

def c(n,k):
    return factorial(n) / (factorial(k) * factorial (n-k))

def c_rec(n,k):
    if k == 1:
        return n
    return c(n-1,k-1) + c(n, k-1)