Sometimes called "kakro" or "cross sums," kakuros are similar to sudokus, but also involve an element of addition. Every white square needs to be filled with a digit from one to nine, as the clues tell you the total of all the digits in that line of boxes.
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KenKen was developed in 2004 by acclaimed Japanese mathematics educator Tetsuya Miyamoto (no, not two guys named Ken). His goal was to improve his students’ math and logic skills... and what better tool than a puzzle? So he developed one that would be understandable, fun, and challenging for anyone at any level. Most importantly, he wanted the puzzle to encourage independent thinking, emphasizing logic, reasoning, concentration, and perseverance. His puzzles immediately met with unbelievable success and are now played the world over by children, adults and the elderly. Since its invention, KenKen has become the world's fastest growing (and most enjoyable) puzzle and has proven to be one of the world's best brain exercises.