用Python求1！-2！+3！-4！+…n！的和（n从键盘输入））

用Python求1！-2！+3！-4！+…n！的和（n从键盘输入）


#阶乘函数  递归
def fn(n):
    if n == 1:
        return n
    else:
        return n*fn(n-1)

n = int(input())
s = 0
flag = 1
for i in range(1,n+1):
    s = s + flag*fn(i)
    flag = -flag
print(s)


n=int(input())
sum1=1
sum2=0
for i in range(1,n+1):
    sum1*=i
    sum2+=sum1
    sum1=-sum1
print(sum2)


import math

n = int(input("请输入整数："))
sum = 0
for i in range(1,n+1):
    factor = (-1)**(i+1)*math.factorial(i)          # math.factorial(9)返回一个数字的阶乘， -1的i+1次方  乘  i的阶乘
    print(factor)
    sum += factor
print("最终结果：",sum)