While KenKen puzzles can be completed on paper, the app KenKen Classic is an easy way for new puzzlers to start. The app provides users with a quick introduction to KenKen puzzles, as well as tools such as “Possible Notes” (numbers that might fill a particular square) and “Impossible Notes” (numbers that cannot be in the square). If you get really stuck, tools like the eye and magic wand, which checks numbers and fills in random squares, can be really helpful. There are 350 total puzzles, with seven different sizes from 3×3 to 9×9 which increase in difficulty. KenKen Classic is available for free in the App Store, and KenKen Classic II is free in Google Play.