欧拉筛模板

const int N = 1e5 + 10;vector<int> prime;
bool st[N];void init() {st[0] = st[1] = 1;for(int i = 2; i < N; i++) {for(int j = 0; j < prime.size() && i * prime[j] < N; j++) {st[i * prime[j]] = 1;if(i % prime[j] == 0) break;}}
}