求阶乘的和

求和1!+2!+3!+...+20!

#include <stdio.h>
int main()
{
    int n, s=0, a=1;
    for (n=1; n<=20; n++)
    {
        a=a*n;
        s=s+a;
    }
    printf("1!+2!+3!...+20!=%d\n", s);
}