When I was younger, we used to be able toget these plastic toys that had numbers on them from 1 to 15. They were in a small square tray with 4 x 4 tiles and the 16 tile was left out. You had to move the tiles around and put the numbers in order. A sort of a 2 dimensional Rubik cube. The other day I made an electronic version, well a static electronic version as I am not clever enough to make it work with a mouse. Here is the image of a local lighthouse
