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Online Sudoku

How to play Sudoku?

Players need to infer all the numbers in the remaining spaces based on the known numbers on the 9×9 board, and satisfy that the numbers in each row, column, and each square (9 spaces each) contain 1 to 9, without repeating.

What is the hardest Sudoku?

According to Finnish mathematician Arto Inkala, the following puzzle of his own invention is the hardest Sudoku puzzle created so far.

Sudoku puzzle