It is an excellent game that really tests your logic and problem solving skills.
Fill in the game board so that the numbers 1 through 9 occur exactly once in each row, column, and 3×3 box.
The numbers can appear in any order and diagonals are not considered.
Your initial game board will consist of several numbers that are already placed.
Those numbers cannot be changed.
Your goal is to fill in the empty squares and depending on the level you choose depends on how many empty squares you have to fill in.
On easy you have to fill in 28-31 empty cells. On medium you have to fill in 38-41 empty cells and on hard you have to fill in 48-51 empty cells.