Renban Sudoku

Renban Sudoku. Marked lines hold consecutive digits in any order — no gaps allowed.

How to play

Fill the 9×9 grid so every row, every column, and every 3×3 box contains the digits 1 to 9 with no repeats — the classic Sudoku rule. Renban Sudoku adds one twist: Marked lines hold consecutive digits in any order — no gaps allowed.

Renban Sudoku adds one or more coloured "renban" lines to the grid, and the cells along each line must hold a set of consecutive digits — a run like 4-5-6-7 — arranged in any order, with no repeats and no gaps. Because the run is unbroken, an L-cell line always carries exactly L consecutive numbers: a 3-cell renban is one of {1,2,3} through {7,8,9}, while a 5-cell renban fills a fixed window such as {2,3,4,5,6}. The spatial order along the line never matters, which is what makes renban sudoku a puzzle about pinning down the range of a line rather than the sequence.

How to solve Renban Sudoku

Start by bounding each line by its length: an L-cell renban uses L consecutive digits, so its highest and lowest digit always differ by exactly L−1, and any candidate outside that window can be struck off. Every digit already placed on a line — or seen by a line cell through its row, column or box — shrinks the run further: put a 6 on a 4-cell line and the whole set must be one of {3-6}, {4-7}, {5-8} or {6-9}, so 1 and 2 vanish immediately. Use the gap as a contradiction check — two placed digits whose difference exceeds L−1 (a 2 and a 7 on a 4-cell line, gap 5 > 3) is impossible, flagging an earlier error. Where two renban lines cross, the shared cell must satisfy both runs at once, so intersecting the two possible windows often collapses both lines to a single set. Long lines are the most constrained of all: a 6-cell renban can only be {1-6}, {2-7}, {3-8} or {4-9}, which locks in the middle digits 4, 5 and 6 no matter which window is correct.

Every Renban Sudoku puzzle is free to play in your browser — no ads, no sign-up, and it works offline.

Frequently asked questions

What is Renban Sudoku?

Renban Sudoku is a 9×9 sudoku with one or more marked "renban" lines drawn across the grid. Every cell on a line must hold a set of consecutive digits in any order — a 3-cell line is a run like 4-5-6, a 5-cell line a run like 3-4-5-6-7 — with no repeats and no gaps. All the normal sudoku rules still apply, so each row, column and box must also contain 1 to 9.

What are the rules of a renban line?

The digits on a renban line must form one unbroken run of consecutive numbers, so an L-cell line uses exactly L consecutive digits and its highest and lowest digit differ by L−1. No digit may repeat on a line, and the run may sit anywhere in 1–9 that fits — a 4-cell line ranges from 1-2-3-4 up to 6-7-8-9. Position along the line is free: the smallest digit need not sit at either end.

Do the digits on a renban line have to be in order?

No — this is the most common misunderstanding. "Renban" fixes which digits appear on the line, not their arrangement, so a 4-cell line holding 3-4-5-6 could read 5-3-6-4 across the cells and still be valid. Work out the consecutive set first, then use each cell's row, column and box to decide where inside the line each digit belongs.