UVa11424 GCD - Extreme (I)

 1 /*by SilverN*/
 2 #include<iostream>
 3 #include<algorithm>
 4 #include<cstring>
 5 #include<cstdio>
 6 #include<cmath>
 7 using namespace std;
 8 const int mxn=200010;
 9 int read(){
10     int x=0,f=1;char ch=getchar();
11     while(ch<‘0‘ || ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}
12     while(ch>=‘0‘ && ch<=‘9‘){x=x*10+ch-‘0‘;ch=getchar();}
13     return x*f;
14 }
15 int pri[mxn],cnt=0;
16 long long phi[mxn],f[mxn];
17 void PHI(){
18     for(int i=2;i<mxn;i++){
19         if(!phi[i]){
20             phi[i]=i-1;
21             pri[++cnt]=i;
22         }
23         for(int j=1;j<=cnt && (long long)i*pri[j]<mxn;j++){
24             if(i%pri[j]==0){
25                 phi[i*pri[j]]=phi[i]*pri[j];
26                 break;
27             }
28             else phi[i*pri[j]]=phi[i]*(pri[j]-1);
29         }
30     }
31     return;
32 }
33 int main(){
34     PHI();
35     int i,j;
36     for(i=1;i<mxn;i++){//枚举因数 
37         for(j=i*2;j<mxn;j+=i){
38             f[j]+=i*phi[j/i];
39         }
40     }
41     for(i=3;i<mxn;i++)f[i]+=f[i-1];
42     while(1){
43         i=read();
44         if(!i)break;
45         printf("%lld\n",f[i]);
46     }
47     return 0;
48 }