poj 1284 Primitive Roots（未完）

Primitive Roots

Description

We say that integer x, 0 < x < p, is a primitive root modulo odd prime p if and only if the set { (xⁱ mod p) | 1 <= i <= p-1 } is equal to { 1, ..., p-1 }. For example, the consecutive powers of 3 modulo 7 are 3, 2, 6, 4, 5, 1, and thus 3 is a primitive root modulo 7. 
Write a program which given any odd prime 3 <= p < 65536 outputs the number of primitive roots modulo p.

Input

Each line of the input contains an odd prime numbers p. Input is terminated by the end-of-file seperator.

Output

For each p, print a single number that gives the number of primitive roots in a single line.

Sample Input

23
31
79

Sample Output

10
8
24

Source

贾怡@pku

 1 #include<iostream>
 2 using namespace std;
 3 int euler(int a){
 4     int i=2;
 5     int ans=a;
 6     if(a%2==0){
 7         //cout<<2<<endl;
 8         ans=ans/i*(i-1);
 9         while(a%2==0){
10               a/=2;
11         }
12     }
13     for(i=3;i<=a;i+=2){//优化
14     if(a%i==0){
15         //cout<<i<<endl;
16         ans=ans/i*(i-1);
17         while(a%i==0){
18               a/=i;
19             }
20         }
21     }
22     return ans;
23 }
24 int main()//23, 28, and 33
25 {
26     int p;
27     while(cin>>p){
28         cout<<euler(p-1)<<endl;
29     }
30     return 0;
31 }