http://www.kenken.com/index.html

Like Sudoku, even though difficulty may vary from puzzle to puzzle, the rules for playing KenKen are fairly simple:

For a 3x3 puzzle, fill in with numbers 1-3.

For a 4x4 puzzle, fill in with numbers 1-4.

For a 5x5 puzzle, fill in with numbers 1-5.

For a 6x6 puzzle, fill in with the numbers 1-6.

For a 7x7 puzzle, fill in with the numbers 1-7.

For a 8x8 puzzle, fill in with the numbers 1-8.

For a 9x9 puzzle, fill in with the numbers 1-9.

Do not repeat a number in any row or column.

The numbers in each heavily outlined set of squares, called cages, must combine (in any order) to produce the target number in the top corner of the cage using the mathematical operation indicated.

Cages with just one box should be filled in with the target number in the top corner.

A number can be repeated within a cage as long as it is not in the same row or column.