UVALIVE 3571 Visible Lattice Points

就欧拉函数然后地推一下。

#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <stack>
#include <queue>
#include <cctype>
#include <cstdio>
#include <string>
#include <vector>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
#define LL long long
#define PI 3.1415926535897932626
using namespace std;
int gcd(int a, int b) {return a % b == 0 ? b : gcd(b, a % b);}
int phi[1010];
int ans[1010];
void calcu()
{
    memset(phi,0,sizeof(phi));
    phi[1] = 1;
    for (int i = 2; i <= 1000; i++)
        if (!phi[i])
      for (int j = i; j <= 1000; j += i)
      {
          if (!phi[j]) phi[j] = j;
          phi[j] = phi[j] / i * (i - 1);
      }
    ans[1] = 3;
    ans[2] = 5;
    for (int i = 3; i <= 1000; i++)
        ans[i] = ans[i - 1] + phi[i] * 2;
}
int main()
{
    int kase = 1;
    int T;
    calcu();
    scanf("%d",&T);
    while (T--)
    {
        int n;
        scanf("%d",&n);
        printf("%d %d %d\n",kase++,n,ans[n]);
    }
    return 0;
}