An example Consecutive puzzle: a bar marks cells that differ by 1 - here 4|5 and 8|9.
Consecutive Sudoku marks the borders between some cells with a short bar. A bar means the two digits either side are consecutive - they differ by exactly 1. In the full version every such pair is marked, so a plain border between two cells is a clue too: it says those digits are not consecutive. Read together, the bars and the gaps solve the grid.
The rule: a bar means "differ by one"
Wherever you see a bar, the two neighbouring digits are a consecutive pair like 4 and 5, or 7 and 8 - in either order. Where there is no bar (in the full version) the neighbours differ by 2 or more. Below, the top two pairs carry bars and the bottom pair does not.
Bars mark consecutive pairs (4-5, 3-4). No bar between 6 and 2 - they differ by more than 1.
Reading a bar
A bar restricts both cells to a consecutive pair: 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8 or 8-9. Every digit has two consecutive neighbours except the extremes - 1 pairs only with 2, and 9 pairs only with 8. That makes the ends of the range the easiest place to start: a bar touching a 9 forces the neighbour to 8, and a bar touching a 1 forces a 2.
A bar on a 9 forces an 8; a bar on a 1 forces a 2 - the extremes have only one consecutive partner.
The negative constraint does the heavy lifting
In a full Consecutive puzzle, the missing bars carry as much information as the printed ones. A blank border beside a 5 rules out both 4 and 6 in the neighbour; a blank border beside a 3 rules out 2 and 4. Every unmarked edge quietly removes two candidates, and on the hardest grids that steady stream of eliminations is what breaks the deadlock - solvers who only use the printed bars grind to a halt.
Solving strategy
- Start at the extremes. A bar on a 1 or 9 forces its partner immediately.
- Follow bar chains. A run of bars is a run of steps of ±1 - like a gentle thermometer that can go either way, it constrains a whole line.
- Mine the blank edges. In the full version, each missing bar removes two candidates from the neighbour - use them relentlessly.
- Feed the grid. Each forced digit behaves like a given for its row, column and box.
Common mistakes
- Reading a bar as an order. A bar never says which side is larger - 4-5 and 5-4 both satisfy it.
- Ignoring the missing bars. In full Consecutive, a blank border is a genuine "not consecutive" clue, not the absence of one.
- Confusing it with a bar that means a ratio. Consecutive bars mean a difference of 1, not a doubling - that is Kropki's black dot, a different variant.
- Forgetting ordinary Sudoku. The bars are an extra layer over the usual row, column and box rules.
Can I play it here?
Not yet - Consecutive 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
Consecutive Sudoku belongs to the comparison 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.