11417 - GCD

Problem A
GCD
Input: Standard Input

Output: Standard Output

Given the value of N, you will have to find the value of G. The definition of G is given below:

Here GCD(i,j) means the greatest common divisor of integer i and integer j.

For those who have trouble understanding summation notation, the meaning of G is given in the following code:

G=0;

for(i=1;i<N;i++)

for(j=i+1;j<=N;j++)

{

G+=GCD(i,j);

}

/*Here GCD() is a function that finds the greatest common divisor of the two input numbers*/

Input

The input file contains at most 100 lines of inputs. Each line contains an integer N (1<N<501). The meaning of N is given in the problem statement. Input is terminated by a line containing a single zero.  This zero should not be processed.

Output

For each line of input produce one line of output. This line contains the value of G for corresponding N.

Sample Input                              Output for Sample Input

10 100 500 0

67 13015 442011

#include<stdio.h>
int gcd(int a, int b)
{
	if(!b) return a;
	return gcd(b,a%b);
}
int main()
{
	int n;
	while (scanf("%d",&n)&&n)
	{
		int g=0,i,j;
		for(i=1;i<n;i++)
			for(j=i+1;j<=n;j++)
				g+=gcd(j,i);
		printf("%d\n",g);
	}
	return 0;
}