Do you like Sudoku puzzles?  The Hadhams website will create you a new puzzle at the foot of every page.

Instructions:

1. Scroll down to the foot of any page on thehadhams.com
2. Select your difficulty level (e.g. 'kids') then click the New button
3. Click in the empty squares and type the missing number
4. When you have filled all the emtpy squares click the Check% button