1040 最大公约数之和(欧拉函数)

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 #define MOD 1000000007
 4 #define INF 0x3f3f3f3f
 5 #define eps 1e-9
 6 #define LL long long
 7 #define MX 1002
 8 #define MK 20002
 9 
10 LL n;
11 LL euler(LL x)
12 {
13     LL res = x;
14     for (LL i=2;i*i<=x;i++)
15     {
16         if (x%i==0)
17         {
18             res=res/i*(i-1);
19             while(x%i==0) x/=i;
20         }
21     }
22     if (x>1) res = res/x*(x-1);
23     return res;
24 }
25 
26 int main()
27 {
28     while (scanf("%lld",&n)!=EOF)
29     {
30         LL ans = 0;
31         for (LL i=1;i*i<=n;i++)
32         {
33             if (n%i==0)
34             {
35                 ans += i*euler(n/i);
36                 if (i*i!=n)
37                     ans += n/i * euler(i);
38             }
39         }
40         printf("%lld\n",ans);
41     }
42     return 0;
43 }