Play the kakuro game. It is like a cross between a crossword and a Sudoku puzzle.
Instead of letters, each block contains the digits 1 through 9. The same digit
will never repeat within a word. If you add the digits in a word, the sum will
be the number shown in the clue. Clues are shown on the left and right sides
of “across” words, and on the top and bottom sides of “down” words.
Click on the numbers in the top right part of the screen to select the number. Click on an empty box to write the number. Click on a previous written number to delete it.

Game is completely controlled by mouse.