欧拉函数模板

#include<bits/stdc++.h>
using namespace std;
int n,k,p[200002],ans;
int cnt,c;
vector<int> v;
void phi()
{
    for(int i=2; i<=n; i++) p[i] = 0;
    p[1] = 1;
    for(int i=2; i<=n; i++)
    if(!p[i]){
        for(int j=i; j<=n; j+=i){
            if(!p[j]){
                p[j] = j;
            }
            p[j] = p[j] / i * (i - 1);
        }
    }
}
int main()
{
    cin >> n;
    phi();
    for(int i=1; i<=n; i++)
    cout << i <<": "<< p[i] << endl;
    return 0;;
}
/*
12 4
1 5 7 11

10 4
1 3 7 9

4 2
1 3

20
1: 1
2: 1
3: 2
4: 2
5: 4
6: 2
7: 6
8: 4
9: 6
10: 4
11: 10
12: 4
13: 12
14: 6
15: 8
16: 8
17: 16
18: 6
19: 18
20: 8
*/