The Number Jumble is a square board with 15 positions, filled by 15 numbered tiles and one gap. At any point, a tile adjacent to the gap can be moved into the gap, creating a new gap position. In other words the gap can be swapped with an adjacent (horizontally and vertically) tile.The objective in the game is to begin with an arbitarary configuration of tiles, and move them so as to get the numbered tiles arranged in ascending order from left to right, with 1 in the top left-hand position.

http://appshopper.com/games/number-jumble