POJ 3090 Visible Lattice Points（欧拉函数）

#include <iostream>
#include <cstdio>
#include <cstring>
#include <string>
#include <algorithm>
#include <climits>
#include <cmath>
#include <ctime>
#include <cassert>
#define IOS ios_base::sync_with_stdio(0); cin.tie(0);
using namespace std;
typedef long long ll;
const int MAX_N = 1010;

int T, n, cases = 0;
ll euler[MAX_N];

void GetEuler()
{
euler[1] = 1;
for(int i = 2; i < MAX_N; i++){
if(euler[i] == 0){
for(int j = i; j < MAX_N; j += i){
if(euler[j] == 0) euler[j] = j;
euler[j] = euler[j] / i * (i - 1);
}
}
}
}

int main()
{
GetEuler();
scanf("%d", &T);
while(T--){
scanf("%d", &n);
ll sum = 0;
for(int i = 1; i <= n; i++){
sum += euler[i];
}
sum = sum * 2 + 1;
printf("%d %d %lld\n", ++cases, n, sum);
}
return 0;
}