500 free puzzles of the fast and smart new 6x6 sudoku variation with extra logic, perfect for mobiles! As first published by Peter Ritmeester in The New York Times July 21, 2019. The rules: insert the digits 1-6 just once in each a) row b) column c) bold outlined area AND d) white and green areas. Sixy Sudoku offer all the fun of regular sudoku, but without the time consuming hard work. Because only digits 1-6 are used, there is instant overview, making errors unlikely. The extra layer of logic makes you think quite hard, but even the toughest Sixys still take much less time than 9x9 sudoku!