The concept of filling a square grid with unique symbols (called a Latin square or magic square) has existed for hundreds of years. The first 9×9 number puzzles began appearing in French newspapers in 1892 (as in the example image below). These puzzles required unique numbers 1-9 in each row and column and inner 3×3 subsquare as well as long the long diagonals. These puzzles all but disappeared from print by the time World War I began.

The modern Sudoku was most likely designed anonymously by Howard Garns, a 74-year-old retired architect and freelance puzzle constructor from Indiana, and first published in 1979 by Dell Magazines as Number Place. He died in 1989 before getting a chance to see his creation as a worldwide phenomenon.

In 1984, Japanese game publisher Nikoli (which will be the subject of a future Puzzlehead article) picked up the idea of Number Place and ran with it. The publisher made two small changes to the concept and renamed it “su-doku”, meaning “single number”. The game became an overnight sensation in newspapers in Japan, possibly because the Japanese language is ill-suited to use in crossword puzzles.

In 1997, New Zealander Wayne Gould was shopping in Tokyo when he picked up a book of sudoku and was instantly hooked. Gould developed a computer program to automatically crank out sudoku puzzles and began selling them on his web site www.sudoku.com. In 2004, he published one of his puzzles in a newspaper in Conway, New Hampshire, and later that year The Times in Britain launched sudoku as a regular feature.

Today, there are many, many variants of sudoku, ranging from different dimensions (such as 2×3 rectangles in a 6×6 grid to 16×16 grids with 4×4 subsquares), oddly-shaped subcells, overlapping puzzles of different sizes, and more. Sudoku has appeared on virtually every medium available, even TV and radio. It has even spawned an annual worldwide competition for die-hard solvers.

Sudoku can be terribly addictive. In Australia in June 2008, a mistrial was declared in a drugs-related jury trial when it was discovered that five of the twelve jurors had been playing Sudoku instead of listening to evidence.

So, what is sudoku, really? The 2 Hot Girls in the Shower have an answer for you. (Don’t worry – despite the name, the link is family friendly.)

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.