递归练习

方法一：
s = 1
sum = 0
for i in range(1,3):
    s = s*i
    sum += s
print(s)
print(sum)

def fn(n):
    if n == 1:
        return 1
    else:
        return fn(n-1) * n
print(fn(3))

def fn(n):
    return 1 if n == 1 else fn(n-1) * n

print(fn(3))



def fn1(n,a=1):
    if n == 1:
        return a
    a = a * n
    return fn1(n-1,a)
print(fn1(3))

def foo(n=10):
    if n == 1:
        return 1
    return (foo(n-1) + 1) * 2

def foo(n=1):
    if n == 10:
        return 1
    return (foo(n + 1) + 1) * 2