#include<iostream>
#include<bitset>
#include<cmath>

using namespace std;

int main()
{
    int const max_number(1000000);
    int const max_test((int)sqrt((double)max_number));
    bitset<max_number+1> numbers;
    numbers.set();
    numbers[0]= 0;
    numbers[1] = 0;
    for(int i(1);i!=max_test;++i)
    {
        if(numbers[i])
        {
            for(int j(i*i);j<max_number+1;j+=i)
            {
                numbers[j]=0;
            }
        }
    }
    cout<<numbers.count()<<endl;
    for(int i(1);i!=1000000;++i)
    {
        if(numbers[i])
        {
            cout<<i<<" ";
        }
    }
    return 0;
}

From liebao