SAN FRANCISCO – Sudoku (search) are deceptively simple-looking puzzles that require no math, spelling or language skills. Unlike crosswords, they don't require an extensive knowledge of trivia. They're logic, pure and simple.
They're also addictive. Sudoku books -- pages and pages of grids with nothing more than numbers in boxes -- are selling so well that they're quickly filling lists of best sellers.
"I can't think of a puzzle book that has sold like this," said Ethan Friedman, who edits The New York Times crossword puzzle books for St. Martin's/Griffin Press (search), including two volumes of sudoku with introductions by Times crossword guru Will Shortz.
"This is a publishing phenomenon," Friedman said. In all, nine sudoku books are planned.
Nielsen BookScan, which lists 10 sudoku titles, estimates that they sold a combined 40,000 copies in the U.S. last week. The only books that sold more were J.K. Rowling's (search) "Harry Potter and the Half-Blood Prince" and Kevin Trudeau's "Natural Cures They Don't Want You to Know About."
Three weeks ago, no sudoku books were on USA Today's top 150 list. Now, there are six.
"I'm not surprised that people like the puzzle -- I thought that was almost certain," said Wayne Gould, a retired judge from New Zealand who wrote a computer program that has helped popularize the puzzles. "I am surprised at how people have gotten into a frenzy about it."
In sudoku, the game is laid out in adjoining grids. Players must figure out which numbers to put in nine rows of nine boxes so that the numbers one through nine appear just once in each column, row and three-by-three square.
The phenomenon originated in 1979, when one of the grids, titled "number place," was published in an American puzzle magazine, according to Shortz, who was curious enough to research its history. The puzzle did not catch on in the United States then, but puzzle enthusiasts in Japan loved the idea. By the early 1980s, the puzzles -- renamed sudoku, which means "single number" -- filled the pages of Japanese magazines.
Enter Gould, a 60-year-old puzzle enthusiast who in 1997 found himself "killing time" in a Japanese bookstore.
"I don't read or write or speak Japanese so there wasn't much that I recognized," he told The Associated Press from his vacation home in Phuket, Thailand. "I picked up a sudoku book and bought it."
He was soon hooked.
"I'd say, 'When I finish this puzzle, I must go mow the lawn.' Then I would finish the puzzle and go on to another one," he said. "I started thinking, 'What happens when I solve all these puzzles?' ... I thought I'd write a computer program so that I'd never run out of puzzles for the rest of my life."
Gould, who had taken up computer programming as a hobby, wrote software that randomly generates the logic puzzles. The grids have only some of the numbers filled in - players must do the rest.
He also wanted to share sudoku with the world - and perhaps "make a bit of money." So one day last November, he marched into The Times of London (search) without an appointment, carrying a copy of that day's newspaper with a square cut out and a sudoku puzzle in its place.
Once Gould persuaded the features editor to come down to the lobby, getting him to publish the puzzles was easy -- he offered to provide them daily for free as long as the paper printed the address of his Web site, where for $14.95 he sells the software needed to generate a lifetime of sudoku -- "endless puzzles made up on the spot, all fresh and original."
The Brits went bonkers. Other newspapers quickly realized that they, too, had to provide sudoku to stay competitive.
And that computer program is about to make him a millionaire, says Gould, who now provides free puzzles to 120 newspapers in 36 countries. Other syndicates provide their own sudoku - Kansas City-based Universal Press (search) and others supply dozens of U.S. newspapers with a daily dose.
The Los Angeles Times started running the puzzles on June 20. The response was immediate, says Sherry Stern, deputy features editor. "It's just something that's captured people," she said. "I can't explain it."
American book publishers saw what was happening in England earlier this year and sensed a big business opportunity.
"There were books on the best seller list there. That was unheard of, to have a puzzle book up on the best seller list," said John Mark Boling, a spokesman for Woodstock, N.Y.-based Overlook Press, which quickly obtained the rights to publish some British sudoku books in the United States. "We beat everyone to the punch, basically."
In July, the first printing of "The Book of Sudoku," by Michael Mepham, sold out in two weeks. Three more sudoku books quickly followed, selling a combined 400,000 copies, Boling said.
"The Book of Sudoku" is also one of two sudoku books on Publishers Weekly's list, at numbers 14 and 15, respectively.
"Our orders go up hourly," Boling said. "We've really been at a rush to keep up with the demand."
At least three more U.S. publishers quickly put out their own sudoku books.
"This is a major league best seller," said St. Martin's Friedman.
New York-based Barnes and Noble (search), the nation's largest bookseller, bought 28,000 sudoku books from Newmarket Press, according to company president Esther Margolis.
"It could flame out, but based on everything I've been able to discern so far, sudoku is a keeper," Margolis said. "It's the kind of puzzle that seems to be so intriguing and satisfies such a wide age range."
Shortz, who has been addicted to sudoku since April, says their appeal is simple.
"Most problems we face in everyday life don't have perfect solutions. It's satisfying to take a problem through to the end all by yourself," he said.
The instructions are short, just one sentence, which Shortz said is "very rare in puzzles."
"It's a tremendous amount of payoff for just the tiny work of understanding what's going on," he said. It's also the perfect size, always nine squares by nine squares. "It's small, but it packs a lot of puzzle in there."
Shortz -- and Gould -- believe sudoku is here to stay.
"It will fade, but I don't expect it to disappear for good," Gould said. "I think the crossword and the sudoku will sit side by side for years to come. The crossword is there for the wordsmith and the sudoku is there for the rest of us."