Keen

Keen is a grid-based puzzle game where the player must fill a grid with numbers, so that each number appears once in every row and column. The grid is divided into regions, each marked with a number clue and an arithmetical operation. The numbers within every region must result in the given number clue when the operation is applied to them (for example, 9+ means that all numbers in the region should add up to 9). Different grid sizes can be chosen. A "multiplication only" mode is available in which there are no operations apart from multiplication.