Sudoku's numbers meet arithmetic cages, fill the grid 1 to N and make every outlined cage hit its target.
Fill an N×N grid so each row and column contains the numbers 1 to N with no repeats. The grid is divided into outlined cages, each showing a target and an operation; the cells in a cage must combine with that operation to reach the target.
The puzzle is Japanese and the famous name is American. It reached the West when the toy inventor Robert Fuhrer came across books published in Japan by the educational publisher Gakken under the title 賢くなるパズル — Kashikoku naru Puzzle, "the puzzle that makes you smart".
Fuhrer's company took a trademark on the brand name KenKen, and with the chess international master David Levy brought the puzzles to Michael Harvey at The Times in London, who was struck by their "depth and magnitude" and began running them in March 2008. Calcudoku is the generic name for the same puzzle.
The design sits one step beyond sudoku. Latin-square rules still apply — every digit once per row and column — but the givens are replaced by cages carrying a target and an operation, so each cage is a small arithmetic problem whose answer is constrained by its neighbours.
Calcudoku is the arithmetic Latin-square logic puzzle, rebuilt as an original, solver-verified free browser game with multiple sizes, difficulties and a daily challenge.