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KenKen, derived from Sudoku, is the latest Japanese number puzzle to appear daily in the New York Times. Will Shortz himself recently wrote an article about the puzzle:

KenKen shares some properties with sudoku. Each is a pure logic challenge in which numbers are filled in the squares of a grid. Unlike sudoku, though, in which the numbers act solely as symbols (letters or pictures would work as well), KenKen requires arithmetic.

The rules are simple: Fill the grid with digits so as not to repeat a digit within any row or column, and so the digits within each heavily outlined box (called a cage) go together using the arithmetic operation shown to make the target number indicated.

What do the Japanese have to say about their new creation?

In recent tests, they [Japanese schoolchildren] have ranked as high as 6th in the world in math skills, 4th in problem solving ability, and 2nd in the application of scientific concepts. Today, these high-achieving students and their parents enjoy a fascinating new pastime: KENKEN™ number puzzle, a unique puzzle that boosts their powers of thinking and calculation, while also increasing their concentration and perseverance.

To solve KENKEN™ number puzzles, you need to add, subtract, multiply and divide. In going through these calculations, your brain continuously tries to find the most effective way to solve the puzzle. In doing so, you exercise your powers of thinking and concentration. Children don’t feel intimated by KENKEN™ number puzzle because it looks like a game, not homework. All they care about is solving the puzzle. And so they calculate … and calculate … and calculate!