Plus Advent Calendar Door #4: Special Sudokus

It's the weekend, the snow is gently falling outside, and inside the fire is blazing ... what better way to spend the time than puzzling over our special Plus sudokus? They're not what you're used to...

Or if you'd rather like to spend your time reading, find out about the history of sudoku, why sudoku puzzles help to take pictures of tiny things like cells, or muse on some sudoku questions that puzzle mathematicians.

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