Sudoku #3609

Level: Extremely Hard

 Fun Fact About 2
Will Shortz, The New York Times crossword editor, told Fortune in October 2005 that "the craze, judging by history, will last four, five, six months, and then it will taper off." He changed his mind by the May/June 2006 issue of Psychology Today and admitted that Sudoku had the staying power of crossword puzzles.

Enter numbers into the empty cells so that each row, column and 3x3 box contains the numbers 1 to 9.