Fifteen - a puzzle , which is 15 square tiles and bears the numbers from 1 to 15. All knuckles are enclosed in square of 4x4 ( side of the square is four times longer than that of the knuckles ) . So when placing tiles in the square remains one blank space the size of a domino , which can be used to move the tiles . The goal - to streamline the placement of numbers, placing them in ascending from left to right and top to bottom , starting with the knuckles with the number 1 in the upper left corner and ending with an empty space in the lower right corner. You can choose a background color and play dominoes . Good luck !