Thanks Alex. I have only recently become a sudoku addict and have discovered that people either love or hate it. There is a positive correlation with people who either love or hate maths. For example, my mother hates maths and won't look at a sudoku because "it's maths". People who love sudoku also tend to love maths. This correlation follows even when the numerals in sudoku are replaced with letters or other symbols, which is just bizarre.

In the latest Australian Mensa journal there was a question asking how many possible valid arrangements are there for completing the sudoku grid? The answer they gave was 6,670,903,752,021,072,936,960. If you remove solutions that could be considered symmetrical, it becomes 5,472,730,538. Don't ask me how they worked it out.