Sudoku geeks gone wild!

This is what happens when professional mathematicians get interested in sudoku -- a fully worked-out theory of the number of possible non-trivial 9 x 9 sudokus, with an investigation into the mathematical structure known as the sudoku symmetry group.

A deceptively difficult puzzle

Sudoku is a form of puzzle that has become hugely popular in recent years. In case you haven't been introduced to it, the basic idea is quite elegant. There is a 9 x 9 array divided into nine 3 x 3 subarrays. Numbers from 1 to 9 are given in some of the cells of the array, and the idea is to complete the whole 9 x 9 array such that

• Every row contains all the numbers 1 - 9.
• Every column contains all the numbers 1-9, and
• Every 3 x 3 subarray contains all the numbers 1 - 9.

It's really addictive, trust me. The best introduction to sudoku solving I know of is this little document (courtesy of sudoku.org).

There are a lot of solution heuristics out there, and a whole bunch of websites devoted to sudoku. I can recommend

• The friendly folks at websudoku.com
• The site sudoku.com, and
• The aforementioned British site sudoku.org, which has a huge number of links, discussions, and solution strategies.