🔵 How to play Odd Sudoku
By Miguel Arechaga
Odd Sudoku is a classic sudoku variant that adds a parity clue: some cells appear shaded (often with a circle) and indicate that only an odd number can go there. It's a very accessible variant and also a great way to learn to reason with parity. Here are the rules and tips.
What is Odd Sudoku?
It's a standard 9x9 sudoku where certain cells are marked as odd. Only the numbers 1, 3, 5, 7 or 9 can be placed in those cells. The remaining cells have no parity restriction and accept any number. The rest of the sudoku rules stay intact.
Rules and how to play step by step
- The sudoku rules apply: 1 to 9 without repeats in each row, column and 3x3 box.
- In the shaded cells (with a circle) you can only write odd numbers: 1, 3, 5, 7 or 9.
- Unmarked cells accept any number. Every puzzle has a unique solution.
Tips to solve Odd Sudoku
- There are only five odd numbers: 1, 3, 5, 7 and 9. A shaded cell already cuts its candidates in half, so they tend to solve sooner.
- Push the even numbers into place: in a row, column or box with several shaded cells, the even numbers (2, 4, 6, 8) are forced into the unmarked cells.
- Count how many odd cells are in each region: if there are exactly five, all of them split up the five odd digits.
- Combine parity with the classic elimination techniques to move faster.
How it differs from regular sudoku
Compared to classic sudoku, Odd Sudoku adds parity information that acts as an extra clue: that's why it usually needs fewer starting numbers. If you enjoy variants with additional restrictions, you'll also enjoy other constraint variants and Sudoku X (Diagonal Sudoku).
