M.: »Absolutely love this app - simple easy to use interface and free.« Opdoku is completely free of charge, with no adverts or additional purchases. Sounds good? Try it out today! The rules are simple: ○ As in Sudoku, each digit can only appear once in each row and column. ○ Each digit is part of a group, each of which has a mathematical operation and a result. All digits in the group have to achieve the specified result using this mathematical operation. Your task is to enter the digits in the grid so that both of these rules are met. Sounds easy? Give it a try! Opdoku is similar to Mathdoku, but with three improvements: ○ If you wish, the puzzle can also have two additional mathematical operations – minimum and maximum. This makes the game more varied and diverse. ○ You can solve puzzles in which only the result of a group is known, but not the mathematical operation. How is 4 reached? Is it 1 + 3, 1 x 4 or 4 / 1? Anything is possible! Hint – 1 is always present. ○ You can even solve puzzles in which not all results of the groups are known. Only geniuses need apply! All Opdoku puzzles have a unique solution. As they are generated automatically a virtually infinite number of puzzles are available. These range from easy ones on a 3x3 grid to virtually impossible ones with barely any clues on a 6x6 grid.