16∙SIXTEEN app for iPhone and iPad
Place numbers from 1 to 16 in right order, like this:
1, 2, 3, 4,
5, 6, 7, 8,
9, 10, 11, 12
13, 14, 15, 16
Tap a black dot to move numbers around it clockwise.
Its easy, isnt it? Or still not?