POJ1284 Primitive Roots (原根)

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
#include<cmath>
using namespace std;

const int N=65536+15;
int p,tot;
int vis[N],prime[N],phi[N];
void get_phi()
{
    phi[1]=1;
    for (int i=2;i<=N;i++)
    {
        if (!vis[i]) 
        {
            prime[++tot]=i;
            phi[i]=i-1;
        }
        for (int j=1;j<=tot&&prime[j]*i<=N;j++)
        {
            vis[prime[j]*i]=1;
            if (i%prime[j]==0) 
            {
                phi[i*prime[j]]=phi[i]*prime[j];
                break;
            }
            else phi[i*prime[j]]=phi[i]*(prime[j]-1);
        }
    }
}
int main()
{
    get_phi();
    while (scanf("%d",&p)!=EOF)
    {
        printf("%d\n",phi[p-1]);    
    }
    return 0;
}