陕西师范大学第七届程序设计竞赛网络同步赛 J 黑猫的小老弟【数论/法拉数列/欧拉函数】

#include<bits/stdc++.h>
#include<cstdio>
#include<string>
#include<cstdlib>
#include<cmath>
#include<iostream>
#include<cstring>
#include<set>
#include<queue>
#include<algorithm>
#include<vector>
#include<map>
#include<cctype>
#include<stack>
#include<sstream>
#include<list>
#include<assert.h>
#include<bitset>
#include<numeric>
#define debug() puts("++++")
#define gcd(a,b) __gcd(a,b)
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define fi first
#define se second
#define pb push_back
#define sqr(x) ((x)*(x))
#define ms(a,b) memset(a,b,sizeof(a))
#define sz size()
#define be begin()
#define pu push_up
#define pd push_down
#define cl clear()
#define lowbit(x) -x&x
#define all 1,n,1
#define rep(i,n,x) for(int i=(x); i<(n); i++)
#define in freopen("in.in","r",stdin)
#define out freopen("out.out","w",stdout)
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
typedef pair<int,int> P;
const int INF = 0x3f3f3f3f;
const LL LNF = 1e18;
const int maxn = 1e3 + 20;
const int maxm = 1e6 + 10;
const double PI = acos(-1.0);
const double eps = 1e-8;
const int dx[] = {-1,1,0,0,1,1,-1,-1};
const int dy[] = {0,0,1,-1,1,-1,1,-1};
const int mon[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
const int monn[] = {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
int n,k,t;
int e[maxm];
int sum[maxm],res = 0;
void init()
{
    ms(e,0);
    e[1]=1;
    for(int i=2;i<=maxm;i++){
        if(!e[i])
        for(int j=i;j<=maxm;j+=i){
            if(!e[j]) 
                e[j]=j;
            e[j]=e[j]/i*(i-1);
        }
    }
}
int main()
{
    init();

    sum[1]=2;
    for(int i=2;i<=maxm;i++)
        sum[i]=sum[i-1]+e[i]; //可以发现，这棵树从中间分开，就是法里数列~法里数列长度f[n]=f[n-1]+φ(n)

    cin>>t;
    while(t--)
    {
        cin>>n;
        cout<<sum[n]<<endl;
    }
}