15 Puzzel Challenge Numbers consists offifteensquares numbered from 1 to 15 which are placed in a 4x4 boxleavingone position out of the 16 empty. The goal is to repositionthesquares from a given arbitrary starting arrangement by slidingthemone at a time into the configuration shown above (for someinitialarrangements, this rearrangement is possible, but forothers, it isnot).

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

It was not surprising that Sam Loyd drove the whole worldcrazyby his variation of the puzzle of 15. The problem thatheformulated was impossible to solve. When you bought Loyd's14-15puzzle the empty square was positioned bottom right. Thepieceswere numbered in order from left to right and from top tobottom;only the pieces numbered 14 and 15 were reversed. Youshouldre-order the pieces so all the pieces are in the correctpositionand the empty place should be positioned bottom rightagain. Aslide puzzle with square pieces can only be solved when thenumberof exchanges necessary to solve the puzzle is even.

A nice variation of the basic slide puzzle is a slide puzzlewith15 pieces numbered form 0 (empty space) to 15 with theinstructionto slide the pieces so that the sum of all rows and thesum of allcolumns and the sum of the diagonals equals 30. Such anordering iscalled a magic square.