Settings → About phone

• https://play.google.com/store/apps/details?id=com.teacapps.barcodescanner - contains ads. See if you can find something that is functionally equivalent but ad free.
• https://play.google.com/store/apps/details?id=com.mobilityware.Sudoku
  • It is 40 MB which is a lot for a sudoku game.

• https://play.google.com/store/apps/details?id=com.Appgeneration.Sudoku
  • It is 59 MB which is a lot for a sudoku game.
  • I did not find a 6×6 version
  • See if you can find something that is functionally equivalent but better