Powered by www.memorij.com 
Explanation Sudoku A Sudoku is a puzzle of 9 by 9 squares, in which a small number of numbers are filled in. The empty boxes must also be filled in. 

The numbers 1 to 9 must occur once in every horizontal row.  
In each block of 3 by 3 the numbers 1 to 9 must occur once.  
The numbers 1 to 9 must appear once in each vertical column. 