题目大意：关于最大公约数(Greatest Common Divisor, GCD)的，直接照着题目说的做就可以了。

1 #include 
      
        2  3 int gcd(int a, int b) 4 { 5     return b == 0 ? a : gcd(b, a%b); 6 } 7  8 int main() 9 {10     int n;11     while (scanf("%d", &n) && n)12     {13         int g = 0;14         for (int i = 1; i < n; i++)15             for (int j = i+1; j <= n; j++)16                 g += gcd(j, i);17         printf("%d\n", g);18     }19     return 0;20 }