Here’s an massively evil game for you to play: Su Doku
If you’ve not played it yet then prepare to lose a lot of time…
It’s got very simple rules:
Each row must have the numbers from 1 to 9 in it
Each column must have the numbers from 1 to 9 in it
Each of the nine 3×3 boxes must have the numbers from 1 to 9 in them
… And that’s it.
Just click on the sample problems to have a go. If you’re new then I strongly suggest the ‘easy’ ones!
(You’ll need Java enabled for the games to run, but if you’re techy enough to know about that then you’ll probably be ready for that anyway.)