POJ1284 Primitive Roots

http://poj.org/problem?id=1284

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

233179

Sample Output

10824

#include<iostream>#include<cstring>using namespace std;int euler(int n){    int i,ans=n;    for(i=2; i*i<=n; i++)        if(n%i==0)        {            ans=ans-ans/i;            while(n%i==0)                n/=i;//把该素因子全部约掉            //while(n%i==0);        }    if(n>1)        ans=ans-ans/n;    return ans;}int main(){    int n;    while(cin>>n)    {        cout<<euler(n-1)<<endl;    }    return 0;}