Digits

Digits is a simple puzzle game. The game objective is to
remove all squares with numbers (1,2,3,4).
The squares are removed in chains.

You can group several
squares in a chain by marking them one-by-one. A new square can
be added to the chain only if it stands next to the previously
marked square (on the right, left, top or bottom, but NOT
diagonally) and if the numbers of all marked squares build up an
increasing or decreasing series. The number of the last marked
square should be greater or less the previous square number by one.