poj1286 Necklace of Beads—— Polya定理

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
typedef long long ll;
int n;
ll ans;
ll pw(ll a,int b)
{
    ll ret=1;
    for(;b;b>>=1,a*=a)
        if(b&1)ret*=a;
    return ret;
}
int gcd(int a,int b){return (a%b==0)?b:gcd(b,a%b);}
ll rot(int n)
{
    ll ret=0;
    for(int i=0;i<n;i++)
        ret+=pw(3,gcd(i,n));
    return ret;
}
ll d(int n)
{
    if(n%2)return (ll)n*pw(3,(n-1)/2+1);
    return (ll)n/2*(pw(3,n/2)+(ll)pw(3,(n-2)/2+2));
}
int main()
{
    while(1)
    {
        scanf("%d",&n);
        if(!n)
        {
            printf("0\n"); continue;//!
        }
        if(n==-1)return 0;
        ans=(rot(n)+d(n))/(2*n);
        printf("%lld\n",ans);
    }
}