A free program for Android, by abbass noon.

243 6×6 Game – Train Your Brain is a brain teaser and puzzle game with a twist. When you play it, you will be challenged to think and solve problems in your head. The idea is to do some mental arithmetic and use your brain power to get to the end of the puzzle. You can play it in four different modes that offer four difficulty levels. The game starts off easy but gets harder as you progress. This is a mathematical game that will test your mind and brain power. If you want to get better at it, then you can train and practice. The game is designed to be relaxing and fun.