求1+2!+3!+...+20!的和。

方法一
#!/usr/bin/python
# -*- coding: UTF-8 -*-

n = 0
s = 0
t = 1
for n in range(1,21):
    t *= n
    s += t
print '1! + 2! + 3! + ... + 20! = %d' % s

方法二
#!/usr/bin/python
# -*- coding: UTF-8 -*-

s = 0
l = range(1,21)
def op(x):
    r = 1
    for i in range(1,x + 1):
        r *= i
    return r
s = sum(map(op,l))
print '1! + 2! + 3! + ... + 20! = %d' % s

以上实例输出结果为：

1! + 2! + 3! + ... + 20! = 2561327494111820313