We’re a reader-funded news organization fighting an expensive lawsuit that threatens our survival. Our reporting remains ...

A Sudoku is a puzzle involving a 9x9 grid into ... These equivalent sets can be very useful for hard Sudokus where all the ...

For the 2017–18 holiday season, we asked you to solve the hardest Sudoku in the world and prove that the solution is unique. We are delighted that even more enthusiastic engineers have shared their ...

All four cells have the same two candidates left (in real Sudoku, not all cells have to hold all of the UR candidates)." ...

Plus, you can let us know what you think of the puzzles by emailing at [email protected]. We look forward to hearing from you.

Sudoku fans, it’s time to really crunch some numbers. Give your mind the ultimate test on the most difficult numbers puzzle each day — and challenge yourself to make the impossible possible.