# Opdoku = Calcudoku + Mathdoku — Challenging, Simple and Funny

> Logic puzzle game combining Sudoku rules with mathematical group operations. (iPhone/iPad app by Christian Rusche.)

- Source: https://appshunter.io/ios/app/opdoku-calcudoku-plus-mathdoku/id1157986223 (this page in markdown: same URL + `.md`)
- Developer: [Christian Rusche](https://appshunter.io/developer/971175500)
- Category: Games, Education, Puzzle, Strategy
- Price: Free
- Rating: 4.20/5 from 10 App Store ratings · 9 written reviews indexed
- Age rating: 4+
- Requires: iOS 15.6 · 0 MB
- Languages: American English
- Released: 2016-09-26
- Data updated: 2026-06-05
- Monetization: free
- User reviews in markdown: https://appshunter.io/ios/app/opdoku-calcudoku-plus-mathdoku/id1157986223/reviews.md

## What is Opdoku = Calcudoku + Mathdoku?

M.: »Absolutely love this app - simple easy to use interface and free.« 
D.: »There's no advertising, they don't ask you for money, and the puzzles are great.« 


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.

## Key features

- Sudoku-like row and column constraints
- Mathematical group operations
- Optional min/max operations
- Unknown mathematical operations
- Unknown group results
- Unique puzzle solutions
- Infinite puzzle generation

## Recent user reviews (9 of 9)

All indexed reviews: https://appshunter.io/ios/app/opdoku-calcudoku-plus-mathdoku/id1157986223/reviews.md

### 5/5 — Challenging, fun, no ads

*2025-11-25*

Love it, but I can't figure out how to turn the possible numbers on.

**Developer response:** Thank you for your feeback! and please press „Show“ on the bottom left to see the possible numbers. Or contact me by using „Feedback“ on the main screen and I will help you.

### 4/5 — Challenging

*2025-01-28*

I love the variety of modes in this game. The UI is clean, easy, and fast to use. I like to play some of the hardest modes. It forced me to think outside the box.

Old request: I would like to have a way to mark possibilities on each tile as opposed to only one number. EDITED: They were nice enough to add this feature, yay!

Ongoing request: I also want to be able to momentarily highlight all numbers of a specific value on the board (both big and small numbers) to make it easier to see what to do next. This will be especially useful for harder puzzles.

**Developer response:** Update: With the new version 6.0, you can now not only mark the possible combinations per group, but also those per digit.

### 2/5 — Missing Features

*2023-02-13, version 5.1*

I love the variety of modes in this game. I would like to have a way to mark possibilities on each tile as opposed to only one number. I also want to be able to highlight all numbers on the board of a specific value to make it easier to see what to do next. This will be especially useful for harder puzzles. I am willing to pay a one time price for these additional features.
Edited: There has not been any updates since the developer's response.

**Developer response:** Update: With the new version 6.0, you can now not only mark the possible combinations per group, but also those per digit.

### 5/5 — Best Kenken app I’ve found.

*2022-10-22*

There are no advertisements, they’re not hounding you for money, and the implementation of the puzzles is great. It’s a breath of fresh air.

**Developer response:** Thank you very much!

### 2/5 — Confusing

*2022-07-12*

The settings are confusing

**Developer response:** With the latest version, I have tried to optimize the start screen and also made help information directly accessible from there.

### 5/5 — Good game

*2021-08-04*

Very fun.

**Developer response:** Thank you for your feedback!

### 2/5 — No note capability

*2021-01-26*

Game does not let you make notes of possible entries in the cell or let you check for errors. Game is ok for small grids but when you get into larger ones it is necessary to have notes.

**Developer response:** With the new version 6.0, you can now not only mark the possible combinations per group, but also those per digit.

### 5/5 — Amazing

*2021-01-16*

Amazing.

**Developer response:** Thank you for your motivating feedback!

### 4/5 — Great but for one small thing

*2018-10-22*

Sometimes it restarts losing your current score

**Developer response:** Thanks for the feedback: I have improved the save function in the latest version. Hopefully this won't happen anymore!

## Frequently asked questions about Opdoku = Calcudoku + Mathdoku

### What is Opdoku?

Opdoku is a free logic puzzle game that combines Sudoku rules with mathematical operations. Players must place digits in a grid so that each digit appears only once in each row and column, and within specified groups that achieve a given mathematical result.

### Does Opdoku have ads or in-app purchases?

No, Opdoku is completely free of charge, with no advertisements or additional purchases. Users have praised its lack of monetization, allowing for uninterrupted gameplay.

### What makes Opdoku different from Mathdoku?

Opdoku offers three improvements over standard Mathdoku: it can include minimum and maximum operations for more variety, puzzles where the mathematical operation is unknown, and puzzles where not all group results are known, increasing the challenge.

### How many puzzles are available in Opdoku?

Opdoku puzzles are generated automatically, providing a virtually infinite number of unique puzzles. The difficulty ranges from easy 3x3 grids to challenging 6x6 grids with minimal clues.

### What devices can I play Opdoku on?

Opdoku is available for iPhone, iPad, and iPod. It is designed to run on Apple's mobile operating system.

### What is the age rating for Opdoku?

Opdoku has an age rating of 4+, making it suitable for young children and players of all ages. The puzzles are designed to be engaging and mentally stimulating.

### How often is Opdoku updated?

The latest version of Opdoku is 6.0, and it was last updated on January 24, 2025. This indicates a recent update, suggesting ongoing support and potential improvements.

### What do users like about Opdoku?

Users love Opdoku for its simple, easy-to-use interface and its completely free nature with no ads or requests for money. The puzzles are frequently described as great and engaging.

## Version history (last 5 releases)

### 6.0 — 2025-01-24

- New start screen with improved help and high score
- New functionality to mark possible solutions per digit
- Puzzles are saved when the application is closed
- Visual and ergonomic improvements: click behavior, screen and font size, etc.

### 5.1 — 2019-01-22

Added a new option that determines whether possible combinations are displayed.

### 5.0 — 2019-01-08

- New game mode with as few information as absolutely necessary.
- Opdoku now shows the possible combinations of each group - and you can also mark them. 
- New feature to save a certain state, then try something and if it doesn't work, rewind everything.
- Better adaptation to iPhone X and smaller screens.

### 4.0 — 2017-02-24

Score and Highscore included

### 3.0 — 2016-12-04

New design

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## More apps by Christian Rusche

- [Kanji Teacher - Learn Japanese](https://appshunter.io/ios/app/kanji-teacher-learn-japanese/id1048445761)
- [Send SOS](https://appshunter.io/ios/app/send-sos/id1088568416)
- [Japanese Keyboard](https://appshunter.io/ios/app/japanese-keyboard/id1532704493)

All apps by Christian Rusche: https://appshunter.io/developer/971175500

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-06-05.*