hdu3501

Problem Description

Given a positive integer N, your task is to calculate the sum of the positive integers less than N which are not coprime to N. A is said to be coprime to B if A, B share no common positive divisors except
1.

Input

For each test case, there is a line containing a positive integer N(1 ≤ N ≤ 1000000000). A line containing a single 0 follows the last test case.

Output

For each test case, you should print the sum module 1000000007 in a line.

Sample Input

3
4
0

Sample Output

0
2

代码如下：

#include <iostream>
#include <cstdio>
using namespace std;
const int mod=1000000007;
int phi(long long m)
{
    long long  rea=m;
    for(long long  i=2;i*i<=m;i++)
     {
         if(m%i==0)
         rea-=rea/i;
         while(m%i==0)
         m/=i;
     }
     if(m>1)
        rea-=rea/m;
     return rea;
}
int main()
{
    /*欧拉函数一个小小的性质：
    求小于n并且与n互质的数的和为：m*phi[m]/2；*/
    long long  m,ans;
    while(~scanf("%lld",&m))
     {
         if(m==0)break;
         ans=phi(m);
         ans=(m*(m-1)/2-m*ans/2)%mod;
         printf("%lld\n",ans);
     }
    return 0;
}#include <iostream>
#include <cstdio>
using namespace std;
const int mod=1000000007;
int phi(long long m)
{
long long rea=m;
for(long long i=2;i*i<=m;i++)
{
if(m%i==0)
rea-=rea/i;
while(m%i==0)
m/=i;
}
if(m>1)
rea-=rea/m;
return rea;
}
int main()
{
/*欧拉函数一个小小的性质：
求小于n并且与n互质的数的和为：n*phi[n]/2；*/
long long m,ans;
while(~scanf("%lld",&m))
{
if(m==0)break;
ans=phi(m);
ans=(m*(m-1)/2-m*ans/2)%mod;
printf("%lld\n",ans);
}
return 0;
}