POJ-1284 Primitive Roots---原根&欧拉函数

 1 #include<iostream>
 2 #include<cmath>
 3 using namespace std;
 4 typedef long long ll;
 5 int euler_phi(int n)//求单个
 6 {
 7     int m = (int)sqrt(n + 0.5);
 8     int ans = n;
 9     for(int i = 2; i <= m; i++)if(n % i == 0)
10     {
11         ans = ans / i * (i - 1);
12         while(n % i == 0)n /= i;
13     }
14     if(n > 1)ans = ans / n * (n - 1);
15     return ans;
16 }
17 int main()
18 {
19     int n;
20     while(cin >> n)
21     {
22         cout<<euler_phi(n - 1)<<endl;
23     }
24     return 0;
25 }