This is a terrific logic exercise.  Logic is a basis for advanced thinking: "If this is true, then, that is true." 
 
 
Parade Magazine contributor, Marilyn vos Savant, created a logic puzzle where an individual, when given a set of numbers within a grid, has to analyze and determine the remaining numbers 1-81.  The numbers may only move numerically by row or column, not diagonally.  When successfully completed, a line drawn from 1-81 will not intersect.  The puzzles are listed by level of difficulty.  They may be played online or printed.
The puzzles have varying degree of difficulty.