Challenge you brain!

On-Core Sudoku: consists of a nine-by-nine grid with 9 inner squares. To solve Sudoku each inner square must have one of the numbers between 1 and 9. Each row and column must contain each number once. It features error checking, annotations (pencil marking), undo move(s) and more.

On-Core Sudoku features:
- Games are generated randomly so you will never play the same game twice.
- The game has three difficulty levels: Easy, Medium and Hard plus a Custom option for custom games.
- Each difficulty level has it's own timer so you can try to beat your best time at each level.
- The game auto-saves so that you can return to it at any time.
- Generate Symmetric or Non-Symmetric puzzles.
- Error checking to show invalid entered numbers.
- Annotate (pencil mark) a tile with one or more numbers.
- Unlimited Undo or Redo moves.
- Autofill option to automatically fill in all the possible annotations.
- Option to enter custom games from sources such as newspapers, puzzle books, websites, etc.
- Wirelessly send or receive custom games, via a local WiFi connection, to a friend or family member who also has Game Pack Volume 1 or On-Core Sudoku.
- Sound effects can be turned on or off.
- No internet connection is required because the games are on your iPhone or iPod Touch.