HDU——T 3501 Calculation 2

http://acm.hdu.edu.cn/showproblem.php?pid=3501

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 4548    Accepted Submission(s): 1878

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

 

Author

GTmac

 

Source

2010 ACM-ICPC Multi-University Training Contest（7）——Host by HIT

 

欧拉函数得和==phi（n)*n/2;

md 还是见识少。。

#include <algorithm>
#include <cstdio>

using namespace std;

#define LL long long
const LL mod(1000000007);
const LL N(1000000000+5);
LL x;

LL phi(LL x)
{
    LL ret=1;
    for(LL i=2;i*i<=x;i++)
        if(x%i==0)
        {
            x/=i;
            ret*=i-1;
            for(;x%i==0;)
                ret*=i,x/=i;
        }
    if(x>1) ret*=x-1;
    return ret;
}

int main()
{
    for(;scanf("%lld",&x)&&x;)
    {
        LL zz=(x-1)*x>>1;
        printf("%lld
",(zz-(x*phi(x)>>1))%mod);
    }
    return 0;
}