Are you experienced? These are the hardest KenKen for super-solvers only!

Acclaimed Japanese mathematics instructor Tetsuya Miyamoto developed KenKen in 2004 with the goal of improving his students math and logic skills. This understandable, fun, and challenging puzzle quickly became a favorite leisure activity for all ages throughout Japan and then for millions of players worldwide. In 2008, Nextoy LLC brought KenKen to the United States, and it soon was the first daily feature since the crossword puzzle to appear in the New York Times. Now its carried in the Los Angeles Times, Chicago Tribune, The Times of London, Scholastic classroom magazines, and more than 100 other national US publications.