How do you do that Sudoku you do?

In its second year as a come-from-nowhere fad in the United States, the fill-in-the-numbers game that looks like the unholy product of a union between a crossword puzzle and the IRS' 1040 tax form is still growing.

Sudoku certainly seems to have a right to make a claim for full-fledged craze status: It has elbowed its way next to the venerable crossword on the horoscope or comics pages of many newspapers; it has inspired countless clubs, groups and fan pages; and there are plenty of stories of workplaces having to ban it because of its power as an addictive time-waster.

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Use a Pencil: Sudoku Tips

But the feather in Sudoku's cap — or, to put it in Sudoku terms, the final digit in that nagging incomplete linked triple — may be that the game is finally getting its own tournament in the United States, and not just for your usual puzzle maniacs.

The First North American Sudoku Tournament will take place at San Francisco's Exploratorium June 3-4.

“What really surprises me and a lot of people is that a lot of people are playing Sudoku who you wouldn't think would,” said 50-year-old puzzlemaker and Discover magazine puzzle columnist Scott Kim, of Half Moon Bay, Calif.

“My mother-in-law is an English teacher and she loves it. These are people who don't like mathematics and are kind of scared by it — math freaks them out. A game has to reach a high level of support to get a tournament, and very few games have reached that: crossword puzzles, Scrabble, bridge.”

Anecdotal evidence seems to suggest that Sudoku is equally popular among men and women, and even leans somewhat toward women, Kim said, suggesting that the numbers game may follow in the footsteps of crossword puzzles, whose fans are about 70 or 80 percent female.

“My theory is that women like putting things in order, have sort of an organized brain,” he said.

Sudoku has many of the hallmarks of a successful puzzle, including accessibility, simplicity and the ability to engage people intellectually without off-putting folks who don't happen to have a Ph.D.

“You need mathematical thinking, critical thinking, but I encourage people to see that the numbers are just symbols,” said Lori Lambertson, a staff teacher at the Exploratorium who specializes in math and science.

“Instead of using the numbers one through nine, I could use the letters of the alphabet, colors or shapes, which makes the puzzle more inviting to people with a fear of things that look too mathematical to them.”

The puzzle is deceptively simple. It's like a checkerboard, only with 81 squares — nine across and nine down — instead of the usual 8x8. And the big 81-square checkerboard is sub-divided into nine squares of nine each — three across and three down.

Each puzzle starts with certain numbers filled in various spots across the grid, either randomly or sometimes in a pattern that's unrelated to the game's solution.

Using those filled-in numbers and the game's only three rules, the puzzle solver must fill in every square in the grid with a number from one to nine.

The rules are as basic as you can get: No column (a vertical line of squares) can have the same number more than once; no row (a horizontal line of squares) can have the same number more than once; and no sub-grid can have the same number more than once.

That's it — but it can be a challenging game that exercises a player's brain and patience.

“It's a game where you gets lots of small victories rather than one big victory when you figure the whole thing out,” Kim said.

Sudoku's rise in the United States was hardly inevitable, even though it actually originated in Indiana.

Based on the Viennese square, a mathematical construct by the 18th-century Swiss mathematician Leonhard Euler, Sudoku, originally called Number Place, was invented in 1979 by Indianapolis man Howard Garns, who, like Rubik of Rubik's cube fame, was an architect. It was published in a puzzle magazine, but it didn't catch on.

In the 1980s, Japanese publisher Nikoli took the idea, modified it slightly and popularized it under a lengthy Japanese name, suuji wa dokushin ni kagiru, meaning roughly “each of
the numbers must occur only once,” shortened to Sudoku.

In 1997, retired New Zealander Wayne Gould noticed a Japanese Sudoku book and was intrigued. The canny Kiwi developed a computer program to create Sudoku puzzles and pitched it to the Times of London (owned by News Corp., the parent company to FOX News), which began printing them in 2004.

By 2005, both the United Kingdom and the United States were fully infected with Sudoku fever. In March a Czech accountant won the first global Sudoku tournament, which was held in Italy.

“It's hard to find someone who hasn't at least seen it if they haven't tried it,” Lambertson said. “I was recently at an international math festival in Costa Rica, and the paper there carries a daily Sudoku.”

Kim, who's working on a pared-down five-by-five version of Sudoku for 5-year-olds, said he believes that Sudoku watchers haven't seen anything yet.

“It hasn't peaked, and in my personal opinion it's going to be a perennial and be here for a long time,” he said.