The 15 Puzzle, also known as Game of Fifteen or Mystic Square, is a sliding puzzle consisting of a frame of numbered square tiles in random order with one tile missing.
The puzzle also exists in other sizes, particularly the smaller 8 Puzzle. If the size is 3×3 tiles, the puzzle is called the 8-puzzle or 9-puzzle, and if 4×4 tiles, the puzzle is called the 15-puzzle or 16-puzzle.
The object of the puzzle is to place the tiles in order by making sliding moves using the empty space. The puzzle is solved when all the tiles have been ordered.