An example Renban puzzle: the pink line holds a run of consecutive digits in any order - here {4, 5, 6, 7}.
Renban Sudoku draws coloured lines across the grid, and each line - a "renban group" - must hold a set of consecutive digits, in any order. A four-cell renban might read 5-3-6-4 along the line, but the digits form the unbroken run 3-4-5-6. There are no repeats and no gaps: it is a straight of consecutive numbers, simply scrambled.
The rule: a scrambled run of consecutive digits
Take the cells a renban line covers, ignore their order, and they must form a run like 3-4-5-6 or 6-7-8-9 with nothing missing and nothing repeated. In the example below the line reads 5, 3, 6, 4 - out of order, but together exactly the run 3 to 6. Every row, column and box still follows the normal Sudoku rules on top of this.
Scrambled along the line (5, 3, 6, 4), the digits form the consecutive run 3-4-5-6.
Think in ranges, not sequences
The order on the line never matters - only the set of values does. That means a renban is really a statement about range: an n-cell renban holds n different consecutive digits, so its highest and lowest values are exactly n − 1 apart. A four-cell renban spans 3, so it must be one of the runs 1-4, 2-5, 3-6, 4-7, 5-8 or 6-9 - and it can never contain both a 1 and a 9, whose gap of 8 is far too wide.
One digit pins the whole run
Because the run is contiguous, a single known digit dramatically narrows it. If a four-cell renban contains a 6, the run must include 6, so it is 3-6, 4-7, 5-8 or 6-9. Every one of those excludes 1 and 2, so those digits vanish from all four cells at once - a large elimination from a single clue.
A four-cell renban holding a 6 must be one of the runs 3-6, 4-7, 5-8 or 6-9 - so 1 and 2 leave every cell on the line.
Solving strategy
- Turn each line into a range. Note its length, then list the handful of runs it could be before looking at anything else.
- Anchor on a given digit. One number on a renban collapses the list of possible runs and usually strikes the extreme digits from every cell.
- Use the units. If a renban lies inside one row or box, its digits cannot repeat anyway - but even crossing units, the consecutive-set rule holds.
- Watch the ends of the number line. Long renbans are pushed toward the middle (a 6-cell line can only be 1-6, 2-7, 3-8 or 4-9), so 1 and 9 are rare on them.
Common mistakes
- Reading the order as the answer. The digits along the line are scrambled; only the set of values matters.
- Allowing a gap. A renban is consecutive - 3-4-6 is not a valid three-cell renban, because 5 is missing.
- Allowing a repeat. The run uses each of its consecutive digits once; no value appears twice on the line.
- Forgetting the span limit. An n-cell renban spans exactly n − 1, which alone rules out the widest digit pairs.
Can I play it here?
Not yet - Renban Sudoku isn't one of the puzzle types SudokuStreak generates for now. But you can learn its rules above, and there's plenty here to sink your teeth into meanwhile:
- Try the closely related X Sudoku, which you can play right now.
- Browse all the Sudoku variants we do offer.
- Or print free puzzles from the printable PDF page.
Where to play it
Renban Sudoku belongs to the constraint family and runs on 9×9. It is not one SudokuStreak generates yet - but the deduction it trains is the deduction every Sudoku runs on.
Difficulty and type are two separate dials here: the type sets the extra rule, the level sets how much of the grid you start with. Hard Sudoku leaves 26 of the 81 cells filled, where scanning gets you started and then leaves you stranded; Expert Sudoku leaves 25, where the beginner tools dry up almost entirely. Take it at the gentler end while the pattern is still new, and move up once it stops being a fight.