The game is a mathematic game,Player touch "new game" to begin the game,one digit square falls during game runing,We call the digit square "moving square"."Moving square" can fall upon a digit square that is under "moving square",we call the digit square "pending square", each row of squaes has a "pending square",the "pending square" at top of a row square.Player can change x coordinate of "moving square" by touching screen."pending square" can clear away if sum of "moving square" and "pending square" is a prime number,then play can score.the "moving square" will become "pending square" if their sum is not prime number.so player should touch screen base "pending square" in order to achieve that sum of "moving square" and "pending square" is a prime number.Player is faild while "pending square" of a row of squares reach the top of screen.