初学者求解？。，，。！。。？！！

Question

Answer 1

供参考:

#include<stdio.h>
long fac(int n)
{
    long s=1;
    int  i;
    for(i=1;i<=n;i++)
        s *= i;
    return s;
}
int main()
{
    int n,i;
    long sum=0;
    scanf("%d",&n);
    for(i=1;i <= 2*n-1;i+=2)
        sum += fac(i);
    printf("sum=%ld",sum);
  
    return 0;
}