练习二十五：阶乘之和计算

阶乘指从1乘以2乘以3乘以4，一直到所求数
表达阶乘是，用“！”表示，例如s得阶乘是s！

求1！+2！+3！+4！+。。。+20！

一般计算

n = int(input("输入数："))
factorial,sum1 = 1,0

for i in range(1,n+1):
    factorial *= i
    sum1 += factorial

print(sum1)

执行结果：

输入数：20
2561327494111820313

用递归来计算：

def factorial(n):
    if n == 1:
        return 1
    if n == 2:
        return 2
    else:
        return factorial(n-1)*n
if __name__ == '__main__':
    from functools import reduce
    n = int(input("输入数："))
    list1 = []
    sum1 = 0
    for i in range(1,n+1):
        list1.append(factorial(i))
    print(list1)
    print(reduce(lambda x,y:x+y,list1))

执行结果：

输入数：20
[1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800, 39916800, 479001600, 6227020800, 87178291200, 1307674368000, 20922789888000, 355687428096000, 6402373705728000, 121645100408832000, 2432902008176640000]
2561327494111820313