30 26 0
3 2
#include <stdio.h>
#include <math.h>
#define maxn 10002
int prime[maxn] = {1, 1};
int main()
{
int i, n, j, ans;
n = sqrt(maxn);
for(i = 2; i <= n; ++i){
if(prime[i]) continue;
for(j = i * i; j <= maxn; j += i)
prime[j] = 1;
}
while(scanf("%d", &n), n){
j = n >> 1; ans = 0;
for(i = 2; i < j; ++i)
if(!prime[i] && !prime[n - i]) ++ans;
printf("%d\n", ans);
}
return 0;
}原文：http://blog.csdn.net/chang_mu/article/details/38085103