推论：小于N且与N互质的所有数的和（包括1）为 N*vola（N）/2
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.
InputFor 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.OutputFor each test case, you should print the sum module 1000000007 in a line.Sample Input
3 4 0
Sample Output
0 2
#include <iostream> #include <cstdio> using namespace std; typedef long long LL; LL n; LL vola(LL x) { LL res = 1; for(LL i=2;i*i<=x;i++) { if(x%i==0) { x/=i; res*=(i-1); while(x%i==0){x/=i;res*=i;} } } if(x>1) res*=(x-1); return res; } int main() { LL n; while(cin>>n&&n) { LL sum = (n*(n-1))/2; sum-=n*vola(n)/2; sum%=1000000007; cout<<sum<<endl; } return 0; }