ImpossiDoku

Sudoku for the determined player.
No childish extra numbers given. Only the ones that is required for a correct sudoku.
Generates sudokus on demand.
Possible to save and load sudokus that you wish to come back to later. These are saved to the memory card, if available, which mean you can send them to friends if it is an extra difficult challenge. Also a fast save to store the current sudoku, so you can try out a number, and then restore the state when you realized it did not work out.

You don't have to press the button if you want to save and exit. It will automatically save the current game when exiting, just use reload in the menu to restore the previous game.

This is the free version. No ads, no stupidity.

The permission request to access external storage (sdcard) is for the ability to save and load sudoku files.