程序代码：

#include <stdio.h>
int fan (int n);
int main ()
{
    int n,s;
    printf("Enter an integer:\n");
    scanf("%d",&n);
    s=fan(n);
    printf("1^2+2^2+...+n^2= %d\n",s);
    return 0;
} // main

int fan (int n)
{
    if(n==1)
        return 1;
    else
        return n*n+fan(n-1);
} // fan

程序代码：

#include <stdio.h>
//gcc编译时取消下行注释
//#include <inttypes.h>

unsigned long long foobar(int n) {
    unsigned long long foo;

    if(1 == n || 0 == n) {
        foo = 1;

    } else {
        foo = foobar(n - 1) * n;
    }

    return foo;
}

unsigned long long add(int n) {
    unsigned long long sum = 0;

    if(1 == n) {
        sum = 1;

    }  else {
        sum = add(n - 2) + foobar(n);
    }

    return sum;
}

int main(void) {
    int n;
    printf("INPUT N: ");
    scanf("%d", &n);

    if(n >= 3 && n % 2 != 0) {
        //gcc编译时取消下行注释
        //printf("1!+3!+...+n! = %"PRIu64"\n", add(n));
        printf("1!+3!+...+n! = %lld\n", add(n));

    } else {
        printf("input arror!\n");
    }

    return 0;
}