汉孤臣の线性筛求欧拉函数之和

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <vector>
#include <queue>
#include <map>
using namespace std;
const int maxn=1000000+50;
int n,m,ans,p[maxn],v[maxn],cnt;
long long o[maxn];
int main()
{
    for (int i=2; i<=maxn-50; ++i)
    {
        if (!v[i]) p[++cnt]=i,v[i]=i,o[i]=i-1;
        for (int j=1; j<=cnt && p[j]*i<=maxn-50 && p[j]<=v[i]; ++j)
        {
            v[i*p[j]]=p[j];
            if (p[j]==v[i]) o[p[j]*i]=o[i]*p[j];
            else o[p[j]*i]=o[i]*(p[j]-1);
        }
    }
    for (; scanf("%d",&n) && n!=0; printf("%lld\n",o[n]));//输入输出略有鬼畜，请见谅
    return 0;
}

模板题：http://private.vjudge.net/problem/POJ-2478

前置知识：积性函数