poj 1284 Primitive Roots

#include<iostream>#include<cstdlib>#include<cstdio>#include<cstring>#include<algorithm>#include<cmath>using namespace std;int phi[66000];int main(){    int i , j ;    for ( i = 2 ; i <=  65536 ; i ++ )        phi[i]=0;    phi[1]=1;    for ( i = 2 ; i <=  65536 ; i ++ )        if ( !phi[i] )        { for ( j = i ; j <=  65536 ; j += i ) {     if ( !phi[j] )         phi[j] = j ;     phi[j] = phi[j] / i * (i - 1 ) ; }        }    int n ;    while ( cin >> n )        cout<<phi[n-1]<<endl;    return 0;}