Here are 33 of maximum difficulty for those of you who accept the challenge. To solve them one must think deep, and use different kinds of logical reasoning. See the developer's page for more information on level 4 sudokus.
If you plan to spend hours on solving sudokus you should definitely afford an ad-free hi-quality App with carefully selected sudokus!
* Library with 33 carefully selected sudokus of maximum difficulty.
* User-interface that also can be operated by fat fingers.
* Unlimited undo- and redo- memory.
* Hi-light all digits of some kind, for exemple all 5:s
* Ability to make small notes in every cell (pencil marks).