2705: [SDOI2012]Longge的问题

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cmath>
 4 using namespace std;
 5 #define LL long long
 6 
 7 int eular(LL n)
 8 {
 9     LL ret=n;
10     LL nn=sqrt(n);
11     for(LL i=2;i<=nn;i++)
12     {
13         if(n%i==0)
14             ret=ret/i*(i-1);
15         while(n%i==0) n/=i;
16     }
17     if(n>1) ret=ret/n*(n-1);
18     return ret;
19 }
20 
21 LL n,ans;
22 
23 int main()
24 {
25     scanf("%lld",&n);
26     LL nn=sqrt(n);
27     for(LL i=1;i<=nn;i++)
28     {
29         if(n%i==0) ans+=i*eular(n/i)+(n/i)*eular(i);
30     }
31     if(nn*nn==n) ans-=eular(nn)*nn;
32     printf("%lld",ans);
33     return 0;
34 }