素数筛

bool isNot[N];
int prime[N],cnt_prime;

void make_prime()
{
    isNot[0]=1;
    isNot[1]=1;
    for(int i=2; i<=N; i++)
    {
        if(!isNot[i])
        {
            prime[cnt_prime++]=i;
            for(int j=2; i*j<=N; j++)
                isNot[i*j]=1;
        }
    }
}