(2)1!+2!+3!+4!+……+n! n=20

以下是Python计算1!+2!+3!+4!+……+n!的方法：

def factorial_sum(n):
    sum = 0
    factorial = 1
    for i in range(1, n+1):
        factorial *= i
        sum += factorial
    return sum

n = 20
result = factorial_sum(n)
print(result)

输出结果为：2561327494111820313