hdu 3501 欧拉函数

 1 #include <iostream>
 2 #include <cstring>
 3 #include <cstdio>
 4 using namespace std;
 5 
 6 typedef long long ll;
 7 const int MOD = 1000000007;
 8 
 9 int euler_phi( int n )
10 {
11     int ans = n;
12     for ( int i = 2; i * i <= n; i++ )
13     {
14         if ( n % i == 0 )
15         {
16             ans = ans / i * ( i - 1 );
17             do
18             {
19                 n = n / i;
20             }
21             while ( n % i == 0 );
22         }
23     }
24     if ( n > 1 )
25     {
26         ans = ans / n * ( n - 1 );
27     }
28     return ans;
29 }
30 
31 int main ()
32 {
33     int n;
34     while ( scanf("%d", &n), n )
35     {
36         int res = ( ll ) ( n - 1 - euler_phi(n) ) * n / 2 % MOD;
37         printf("%d\n", res);
38     }
39     return 0;
40 }