def factorial(n):
    result = n
    for i in range(1,  n):
        result *= i
    return result
number = int(input("请输入一个正整数："))

result = factorial(number)
print("%d的阶乘是：%d" %(number, result))

-----

def factorial(n):
    if n == 1:
        return 1
    else:
        return n* factorial(n - 1)
number = int(input("请输入一个正整数："))

result = factorial(number)
print("%d的阶乘是：%d" %(number, result))

斐波那契数列

def f(n):
    if n == 1:
        ret = 0
    elif n == 2:
        ret = 1
    else:
        ret = f(n-1)+f(n-2)
    return ret
print(f(4))
def f(n):
    if n == 1:
        return 0
    elif n == 2:
        return 1
    return f(n-1)+f(n-2)
print(f(5))