sliding squares puzzle

Green flag to play.
3 and 4 buttons to switch between 3x3 and 4x4 game.
Click a number to slide it into the empty space. Arrange the numbers like this
1 2 3
4 5 6
7 8

Or, for the 4x4 game
1   2   3   4
5   6   7   8
9  10 11 12
13 14

There's no fanfare to signal when you have  completed the game - just your sense of satisfaction.