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https://blog.csdn.net/u011328934/article/details/36644069

题目大意：H-number为4∗k+1(k为非负数)，H-composites为因子中含有H-number(不包含自己本身)的数。反之久是H-prime，给定n。求有多少H-composites。

解题思路：首先用筛选法求出范围内的H-prime。然后枚举两个推断乘积是否在范围内。

#include 
      
       #include 
       
        const int maxn = 1e6+5;typedef long long ll;int v[maxn], prime[maxn], cp;void primeHtable(int n) {    cp = 0;    memset(v, 0, sizeof(v));    for (int i = 5; i < n; i += 4) {        if (v[i])            continue;        prime[cp++] = i;        for (int j = i * 2; j < n; j += i)            v[j] = 1;    }}int solve (int n) {    int ans = 0;    memset(v, 0, sizeof(v));    for (int i = 0; prime[i] < n && i < cp; i++) {        if ((ll)prime[i] * prime[i] > n)            break;        for (int j = i; prime[j] < n && j < cp; j++) {            ll u = (ll)prime[i] * prime[j];            if (u > n)                break;            if (v[u])                continue;            ans++;            v[u] = 1;        }    }    return ans;}int main () {    primeHtable(maxn);    int n;    while (scanf("%d", &n) == 1 && n) {        printf("%d %d\n", n, solve(n));    }    return 0;}