It’s simply a matter of trading one piece for another until your cube looks something like this:

Teachers magazine has recommended Sudoku as brain exercise in classrooms. It has even been suggested that it can slow the progression of conditions such as Alzheimer's.

: 'Mobile Su Doku; The game everyone's talking about - now on your mobile phone'. Yesterday's Independent dangled the prospect of becoming a 'Grand Master' in the first Sudoku Championship of Great Britain, and BBC Radio 4's Today read numbers aloud in the first radio version

This is light relief and anybody, including immigrants who don't speak the native language, can do it.

We decided to feature it more and produced a complete book of Number Place puzzles. But we didn't suspect it would become a global phenomenon.'

the difference for Sudoku players is that the grid is subdivided into blocks of nine.

Scientists have identified Sudoku as a classic meme

National newspapers scrambled to advertise the puzzle on their front pages, while websites devoted to it sprang up and TV and radio stations caught the new global bug.