Number of rectangles

Problem solving with programming: Number of rectangles
Given a number of unit squares (1 x 1). How many different rectangles can be formed with them?

For example let us consider 4 units. We can form 5 different rectangles like the following. Two rectangles are considered same if they are oriented in a different way but same dimensions.

Basically we have to arrange 1 to N-1 units to form rectangles of different dimensions. 
This boils down to finding the sum of the number of pairs factors of 1 to N numbers.

 cin >> n;


 int i,j;


 int r = 0;


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


 {


  for( j = 1; j <= sqrt(i*1.0); j++ )


  {


   if( i % j == 0 )


    r++;


  }


 }


 cout << r << endl;

Read full article from Problem solving with programming: Number of rectangles