All Sudoku Variants
9×9 · Constraint

Battenburg Sudoku

Also known as Battenberg Sudoku

Marked 2×2 areas must show a chequerboard of odd and even digits, like the squares of a Battenberg cake.

5 2 4 7 1 9

An example Battenburg puzzle: around the marked point the four cells alternate odd (pink) and even (yellow) — 5, 2, 4, 7.

Battenburg Sudoku marks certain points where four cells meet. At every marked point, those four cells must alternate odd and even like a chequerboard — just like the pink-and-yellow squares of a Battenberg cake. Diagonally opposite cells share a parity; side-by-side cells are opposite.

The rule: a 2×2 chequerboard of parity

Look at the four cells around a Battenburg mark. Two diagonally opposite cells are even, the other two are odd — so no two cells sharing an edge have the same parity. Below, 6 and 8 (even) sit on one diagonal, and 3 and 5 (odd) on the other.

6 3 5 8

Even on one diagonal (6, 8), odd on the other (3, 5) — a chequerboard.

A worked example, step by step

Suppose one corner of a Battenburg mark is already a 6.

6

Step 0. One corner is a 6 (even).

Step 1 — the diagonal partner is even. The cell diagonally opposite the 6 shares its parity, so it must be even too (2, 4, 6 or 8).

Step 2 — the side cells are odd. The two cells next to the 6 are the opposite parity, so both must be odd (1, 3, 5, 7 or 9). One placed digit fixes the parity of the whole 2×2.

6 odd odd even

Step 2. Diagonal partner even; the two side cells odd — the whole square's parity is set.

Why parity is powerful

Fixing parity halves the candidates in each of the four cells at a stroke: an "even" cell drops 1, 3, 5, 7 and 9, and an "odd" cell drops 2, 4, 6 and 8. Combined with the ordinary rules — and with any sum or comparison clues nearby — that often turns the 2×2 into a cluster of near-singles. Battenburg marks are small but they punch above their weight.

Solving strategy

  • One digit sets the pattern. Any placed value in a marked 2×2 fixes the parity of all four cells.
  • Prune by parity. Pencil only even digits into even cells and only odd into odd ones.
  • Combine with other clues. Parity plus a sum or inequality nearby frequently pins exact digits.
  • Feed the grid. Each digit placed behaves like a given for its row, column and box.

Common mistakes

  • Same parity side by side. Edge-sharing cells must be opposite parities — never both even or both odd.
  • Applying it to unmarked junctions. Only the marked meeting points carry the chequerboard rule.
  • Forgetting 5 is odd. The middle digit trips people up — it belongs in odd cells.
  • Ignoring ordinary Sudoku. The four cells still obey their rows, columns and boxes.

Can I play it here?

Not yet — Battenburg 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: