A recent mathematics study showed that you have to have at least 17 clues on a Sudoku grid in order for the puzzle to be solvable. You could make the game easier, by adding more clues. But if there are fewer than 17 clues, then the game becomes impossible to solve. In this video, mathematician James Grime explains how the researchers figured this out.
Maggie Koerth-Baker is the science editor at BoingBoing.net. She writes a monthly column for The New York Times Magazine and is the author of Before the Lights Go Out, a book about electricity, infrastructure, and the future of energy. You can find Maggie on Twitter and Facebook.