A Sudoku is a logic puzzle. The rules are simple. You have a 9 by 9 grid which is split into 9 equal sized boxes (3 by 3). In each row, column and box you have to write the numbers 1 to 9 (in any order). No mathematics is involved, so it is similar to a magic square puzzle but not the same.

You can't have the same number twice in a row, column or box. When the puzzles are created you are given some numbers to start with. Using these numbers you have to work out where the other numbers go.

For instance say I had a 2 in the top row of the grid and a 2 in the next box one row down. This means that the 2 can only go in the third box, along the bottom row.

It maybe easier to understand with a diagram:

I have a 2 in the top row and in the middle row. This means the 2 has to go where I've put the stars:

??2 | ?6? | ?89
?45 | ??2 | ?7?
?7? | ?56 | ***

Sudoku software can be found at www.sudoku.com. The software is sold by Pappocom (a one man software company run by Wayne Gould).

Sudoku puzzles can also be found in the Times Newspaper.

Note: There's a little mistake in the diagram. See if you can spot it.