Renban Sudoku: rules, strategy and how to start
A renban line holds a run of consecutive digits in any order. It is the only line variant where order carries no information at all — only the set does.
Why the rule changes everything
Because order is free, a renban constrains the set of digits without saying which cell holds which. A three-cell renban is always {1,2,3} or {2,3,4} … or {7,8,9} — nine possible sets, and the surrounding sudoku eliminates most of them.
The strongest deduction is the boundary: a four-cell renban that sees a 1 and a 2 elsewhere cannot use {1,2,3,4}, so it shifts up.
How to start a board
- Count the line length. A three-cell renban cannot contain 1 and 9 together — the span would be nine, not three.
- Look for cells on the line that already see several digits; each elimination removes a whole set.
- On long renbans, find the min and max first. Everything else is bracketed between them.
Common mistakes
- Assuming the digits appear in order along the line (that is a thermo, not a renban).
- Placing a digit that breaks the span: any digit placed on a renban must leave room for the missing values on both sides.
- Ignoring that renban digits are distinct by definition — a duplicate immediately disproves the set.
Frequently asked questions
Is a two-cell renban the same as a white Kropki dot?
Yes — two consecutive digits, either order.
Can a renban wrap from 9 back to 1?
No. Renbans are linear runs of consecutive values, not circular.
Every board on this site is generated with a uniqueness check, so the puzzle in front of you has exactly one solution and every digit can be proved rather than guessed.
Play Renban Sudoku ↗