线性筛

强行草率的放上代码：

#include <iostream>
#include <cstdio>
#include <queue>
#include <cstring>
using namespace std;

const int MAXN = 10000000;
int n, cnt = 0;
int prime[MAXN];
bool vis[MAXN];

void solve()
{
    for(int i = 0; i <= n; i ++)
        vis[i] = 1;

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

void print()
{
    cout << cnt << endl;
    for(int i = 1; i <= cnt; i ++)
        printf("%d ", prime[i]);
    cout << endl;
}

int main()
{
    cin >> n;
    solve();
    print();
    return 0;
}