Logic Masters Deutschland e.V.

Place the digits 1 to 9 in every row and column. The digits in each outlined group of cells, - often called "cages" -, must produce a certain "target" number in the top left corner, when combined using the specified mathematical operation (either addition, subtraction, multiplication or division). Digits may be repeated within a given cage, as long as they are not in the same row or column.

This puzzle is also known very famously as KenKen or KenDoku. It is invented in 2004 by the Japanese math teacher Tetsuya Miyamoto, an innovator who says he practices "the art of teaching without teaching".