数学

  static void sai(int n) {

        for (int i = 2; i <= n; i++) {
            if (check[i] == 0) {
                prime[cnt++] = i;
            }
            for (int j = 0; j < cnt; j++) {
                if (i * prime[j] > n)
                    break;
                check[i * prime[j]] = 1;
                if (i % prime[j] == 0)
                    break;
            }
        }
    }

素数筛

https://www.cnblogs.com/grubbyskyer/p/3852421.html