Grid Play - Sudoku
Sudoku is a 9 by 9 grid game utilizing the logic based placement of numbers in the grid. The modern game was constructed by American Howard Garns but its popularity in Japan, before gaining traction in the USA, makes most people equate the origin of the modern game as Japanese. Sudoku is an excellent game to exercise the brain.
Use the Wikipedia link below to learn more about Sudoku.
Sudoku - Wikipedia, the free encyclopedia
Math.com Sudoku - New Puzzle Each Day
American Scientist Online - Unwed Numbers of Sudoku