Play Killer Doublers Sudoku Online Free

Play Killer Doublers Sudoku online for free. Killer cages combined with 9 doubler cells whose digits count 2× toward cage sums. A famous CTC variant.

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How to Play Killer Doublers Sudoku

  1. Standard Sudoku rules: rows, columns, and 3×3 boxes contain 1-9.
  2. Dotted cages show a target sum — digits inside must add up to that sum.
  3. No digit can repeat within a cage.
  4. 9 cells are marked with small yellow dots — these are 'doublers'.
  5. Doubler cells contribute 2× their digit value to their cage's sum.
  6. Exactly one doubler appears in every row, column, and 3×3 box (Latin permutation).
💡 Pro Tip
If a cage sum exceeds what's possible from 9 distinct digits ({1..9} = 45), the cage MUST contain a doubler. Use this to identify doubler positions and the digits they hold.

Frequently Asked Questions

How do doublers affect the cage sum?

When computing a cage's sum, the digit in a doubler cell counts twice. For example, a doubler holding 7 contributes 14 to the cage sum.

Can a cage have multiple doublers?

Yes. There are 9 doublers total across the grid (one per row/column/box), but a single cage might contain multiple of them — boosting the cage sum significantly.

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