编写函数main，求3!＋6!＋9!的结果

def main():
    s = 0
    for i in range(3, 22, 3):
        x = 1
        for j in range(1, i + 1):
            x *= j
        s += x
    return s

print(main())

a=1;b=0
for i in range(1,22):
    a*=i
    if not i%3:
        b+=a
print(b)