Popular puzzle game.
Popular puzzle game invented in 1878 by Noah Chapman. Is a set of identical square tiles with applied numbers, enclosed in a square box. The length of the box four times the length of tiles for a set of 15 elements, respectively, in the box is left blank a square field. The purpose of the game - moving the tiles on the box to achieve their ordering by number, preferably by making the least possible moves.
The application has 4 difficulty levels, from three to six rows of the tiles.