Rules: Standard Sudoku rules (insert a number in the indicated range into each cell so that no number repeats in any row, column, or bold region). Also, cells with a square contain an even number; cells with a circle contain an odd number.

Answer String: Enter the row/column marked “A”, followed by a comma, followed by the row/column marked “B”. Rows are entered from left to right and columns from top to bottom. This example has the key “687345129,546791238”.

(Brief) History of Even/Odd Sudoku: Descended from Sudoku, as a variation that includes number properties as additional limits in the cells.

History of this example: This Even/Odd Sudoku “Ring Cycle” was written by Thomas Snyder for our Grandmaster Puzzles blog post on 1/29/2015.

Sources for Even/Odd Sudoku: Follow this link for Even/Odd Sudoku puzzles on this website. If you are new to this puzzle type, here are our easiest Even/Odd Sudoku to get started on. More Even/Odd Sudoku puzzles can be found in The Art of Sudoku 2 and Masterpiece Sudoku Mix 1.

Design rules for contributors: A Grandmaster Even/Odd Sudoku will have a unique solution that can be reached by logic alone. Generally, a Grandmaster Even/Odd Sudoku has a symmetric layout of numbers and a symmetric or thematic layout of marked even/odd cells in the grid.