C++ 为啥打表不行呢？？？

#include <cstdlib>
#include <iostream>
using namespace std;
bool prime[20005];
int n, i, j;
int main(int argc, char *argv[])
{
    cin >> n;
    for (i = 1; i <= 20000; i++)
      prime[i] = true;
    for (i = 2; i <= 10000; i++)
      for (j = i; j <= 20000; j += i)
        prime[j] = false;
    for (int a = 2; a <= n - 4; a++)
      for (int b = 2; b <= n - 4; b++)
      {
        int c = n - a - b;
        if (prime[a] && prime[b] && prime[c])
        {
          cout << a << " " << b << " " << c << endl;
          break;
        }
      }
    system("PAUSE");
    return EXIT_SUCCESS;
}