Sudoku variants through history
Within a few years of Sudoku reaching newspapers in 2004, publishers were printing versions with other grid sizes, extra constraints and arithmetic. Some have traceable histories: killer Sudoku is credited to the Tokyo puzzle setter Tetsuya Nishio and reached The Times in 2005.
16×16 puzzles had appeared in Dell’s Number Place Challenger and in the Radio Times by August 2005. For other variants, including hyper and anti-knight Sudoku, the sources opened for this page give no dated first appearance, so this page does not invent one.
What counts as a variant?
A variant keeps the central idea of Sudoku, filling a grid so that no digit repeats within a group, and changes something about the grid or the groups. A survey of the field in the encyclopedia article used here sorts the changes into several kinds: different sizes and region shapes, extra limits on where numbers can go, arithmetic constraints, and puzzles built from several overlapping grids [1]. That is also how this page is organized.
Different sizes and region shapes
The 9×9 grid with 3×3 boxes is by far the most common, but the same article lists many alternatives [1]:
- 4×4 grids with 2×2 regions, and 6×6 grids with 2×3 regions. The World Puzzle Championship has featured a 6×6 grid with 2×3 regions, and a 6×6 “Mini Sudoku” with 3×2 regions appears in the American newspaper USA Today. A BBC game show launched in 2005, SUDO-Q, used only 4×4 and 6×6 puzzles, and ran four seasons before ending in 2007.
- 5×5 grids with pentomino regions, published under the name Logi-5, and a 7×7 grid with heptomino regions that has been used in the World Puzzle Championship.
- 12×12 grids with 4×3 regions, which The Times prints as “Dodeka Sudoku”.
- Larger grids: Dell Magazines regularly publishes 16×16 “Number Place Challenger” puzzles using the numbers 1 to 16 or the letters A to P. Nikoli offers 25×25 “Sudoku the Giant”, and a 100×100 puzzle called “Sudoku-zilla” was published in 2010.
- Irregular regions, known under several names including Suguru, Tectonic and Jigsaw Sudoku.
The Radio Times printed a weekly 16×16 “Super Sudoku” from 2 August 2005, within a year of the first British newspaper Sudoku [1]. The 16×16 board on this site uses the symbols 1 to 9 and A to G rather than Dell’s A to P, a choice of this site and not a historical rule.
Extra limits on placement
Another common variant adds a limit beyond the usual row, column and box rules, and the most frequent version requires the two main diagonals to hold each digit once. The encyclopedia article says Dell’s Number Place Challenger puzzles are all of this diagonal type, and that “sudoku X” puzzles in the Daily Mail use 6×6 grids [1]. The diagonal board here follows the same diagonal rule on a 9×9 grid.
For the hyper variant, with four extra windows, and the anti-knight variant, which bars equal digits a chess knight’s move apart, none of the sources opened for this page gave a dated first appearance or an inventor. This page therefore says nothing about when or by whom those were created. The rules the site uses for them are stated on the rules page, as this site’s implementation.
Arithmetic: killer Sudoku
Killer Sudoku combines Sudoku with elements of the Japanese sum puzzle kakuro. Its invention is usually credited to the Tokyo-based puzzle setter Tetsuya Nishio, who developed it from an idea of one of his students, Miyuki Nisawa [2]. In Japan it is called samunamupure, “sum number place”. It first appeared outside Japan in The Times in 2005, with a Times article of 31 August 2005 cited as an early record, and it now appears regularly there and elsewhere [2].
The standard form divides the grid into cages whose digits must add up to a stated total, with no digit repeated inside a cage [2]. Some details differ from this site’s version. In the usual form described in the source, the grid starts empty, with no given digits, and cages can have between two and nine cells; the source adds that the no-repeat rule was not always stated in early puzzles [2]. The stored killer puzzles here are generated with cages of up to five cells and a handful of givens, between none and ten. The source also describes the arithmetic tricks that the killer board relies on, such as the fact that every row, column and box sums to 45, which gives rise to “innie” and “outie” cells [2].
The same article records two hybrids: Killer Sudoku-X, which adds the long diagonals, and Killer Jigsaw Sudoku, which replaces the boxes with irregular regions of equal size [2].
Several grids at once
Five 9×9 grids overlapping at their corner regions, arranged like the five on a die, are called Gattai 5 in Japan, meaning “five merged”. The Times, The Age and The Sydney Morning Herald call this form “Samurai Sudoku” [1]. The same article lists three-dimensional puzzles, such as one published in The Daily Telegraph in May 2005 and the Tredoku puzzles in The Times, as well as a Sudoku version of the Rubik’s Cube, and logic variations such as Greater Than Sudoku [1]. None of these is on this site.
Daily puzzles and difficulty tiers
Two features of this site come from newspaper tradition. After launching in November 2004, The Times began printing an easy and a difficult puzzle side by side on 20 June 2005 [1]. Offering levels is therefore as old as the puzzle’s newspaper life. A shared daily puzzle, the idea behind the daily Sudoku, follows the newspaper habit of one puzzle per day for all readers. The sources opened here do not trace the first daily online Sudoku, so no date is given for that.
How this site’s boards relate to the history
| Board | What the sources opened for this page say |
|---|---|
| 4×4 | 4×4 grids with 2×2 regions exist, and a BBC game show used 4×4 and 6×6 puzzles [1] |
| 6×6 | Appears in the World Puzzle Championship and as Mini Sudoku in USA Today [1] |
| Killer | Credited to Tetsuya Nishio; in The Times from 2005 [2] |
| Diagonal | The most common extra-limit variant [1] |
| Irregular | Exists under names such as Jigsaw Sudoku; no date found [1] |
| Hyper | No dated source opened; nothing claimed |
| Anti-knight | No dated source opened; nothing claimed |
| Daily | Newspaper tradition of one puzzle a day; no first date found [1] |
| 16×16 | Dell’s Number Place Challenger; Radio Times Super Sudoku from August 2005 [1] |
| Expert mode | A feature of this site, not a historical variant |
What this page does not cover
This is a short survey from two encyclopedia articles, not a complete history of every variant. Dates and attributions should be checked against the references those articles cite, such as the Times article of 31 August 2005 and Will Shortz’s 2006 book on Sudoku variations, neither of which was opened here. For the main story, see the history of Sudoku, and for the rules of each board, the rules page. The history hub lists all four history pages, and the games hub has the playable boards.
Sources
- “Sudoku.” Wikipedia. https://en.wikipedia.org/wiki/Sudoku. Accessed 22 October 2026.
- “Killer sudoku.” Wikipedia. https://en.wikipedia.org/wiki/Killer_sudoku. Accessed 22 October 2026. The article cites Leo Lewis, “Too good for Fiendish? Then try Killer Su Doku”, The Times, 31 August 2005, and Will Shortz, Will Shortz’s Favorite Sudoku Variations (St. Martin’s Griffin, 2006); neither was opened for this page.