The 15 puzzle is a sliding puzzle that consists of a frame of 4x4 numbered square tiles in random order with one tile missing. The object of the puzzle is to place the tiles in order (see diagram). It's also called Gem Puzzle, Boss Puzzle, Game of Fifteen, Mystic Square.

The aim of the game is to move the tiles so that they are in order from 1 to 15 with the blank at the lower right.
Clicking on a tile will move it, provided it is adjacent to the blank.

The puzzle was "invented" in USA by Noyes Palmer Chapman, a postmaster in Canastota, New York in 1878.
The game became a craze in the U.S. in February 1880, Canada in March, Europe in April.
Feel free to mail me.
Any suggestions are welcome.