So. You think you’re smart. Well, Finnish mathematician Arto Inkala challenges you to a game of sudoku, the hardest one ever constructed (on the scale of 1 to 5 as rated by difficulty, this sudoku goes all the way to eleven):

6160873852sudoku.jpg 445x350 The World’s Hardest Sudoku

See the rest here:
The World’s Hardest Sudoku