Fill a 3x3 square with the numbers from 1 to 9, so the four sides and the two diagonals share the same sum, which is to be as large as possible.

 6  5  7
 4  3  2   = 18
 8  1  9

This is the only square with sides and diagonals equal to each other.  There are, of course, reflections and rotations of this square.

Posted by Erik O. on 2004-06-22 09:24:52