The World’s Most Infectious Puzzle

How popular is Sudoku?

It's a monster. Barely a year after its introduction to the West, this unassuming little puzzle can now be found in more than 140 newspapers around the world, including at least 30 in the United States. Amazon.com sells 193 Sudoku books, ranging from Su Doku for Dummies to Killer Su Doku (spelling varies by publisher). In a typical week, there are 7 Sudoku books on the USA Today top 150 best-sellers list. Fanatics can also buy Sudoku calendars, board games, and jigsaw puzzles, and download Sudoku grids to their mobile phones. Psychologist Susan Blackmore calls Sudoku a classic meme, an idea that spreads rapidly from one person to the next. 'œIt is using our brains to propagate itself across the world like an infectious virus.'

Why did it catch on?

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'œThe beauty of Sudoku is that it is so easy to grasp the concept, yet it has depth,' says Nobuhiko Kanamoto of the Japanese puzzle publisher Nikoli. Every Sudoku puzzle starts with a nine-by-nine grid, subdivided into nine three-by-three regions. The goal is to fill the 81 squares with numbers from one to nine in such a way that each row, column, and three-by-three region contains exactly one of each number. Each puzzle starts with a certain number of squares already filled in; how many is one of the factors that determines the level of difficulty. An average puzzler can do an easy grid in 10 minutes, while a tricky one might take an hour or more. One thing that makes the puzzles appealing is that despite all the numbers, there's no arithmetic required. Indeed, there are versions for children that use pictures instead of numbers. Solving a Sudoku is basically a matter of scanning the grid for patterns. A true Sudoku can have only one possible solution, and it is unforgiving of mistakes. Catch an error too late and you often have to erase everything and start from scratch.

Who came up with this?

Not the Japanese. Modern Sudoku began life in the United States as Number Place, an occasional feature of Dell puzzle magazines in the late 1970s. The puzzle was imported to Japan in 1984 by Nikoli's Kanamoto, who tweaked it slightly and renamed it Suuji Wa Dokushin Ni Kagiru, or The Numbers Must be Single. Sudoku'”as it was soon being called'”had an advantage in Japan that Number Place did not have in the U.S.: The Japanese alphabet is poorly suited to crossword puzzles, so Sudoku was able to take root with little competition. But if Japan didn't invent Sudoku, America can't take complete credit either. Sudoku evolved from Latin squares, which was created by Swiss mathematician Leonhard Euler in 1783.

How did it get back to America?

In 1997, a 52-year-old New Zealand judge named Wayne Gould, who was living in Hong Kong, became hooked on Sudoku during a trip to Tokyo. He spent the next six years writing a computer program that could create the puzzles. In October 2004, he pitched Sudoku to the London Times. 'œI turned up unannounced at the Times like an old-fashioned traveling salesman,' Gould says. The newspaper's features editor, Mike Harvey, asked an aide to send Gould away. 'œBut he said he was too busy so I went down myself,' Harvey says. 'œIt took about two minutes for him to persuade me.' It helped that Gould was offering to give his puzzle away for free. All he wanted in return was a plug for his Web site, Sudoku.com, where he sells his computer program for $14.95. The Times began running Sudoku in November 2004. Three days later, the London Daily Mail had its own version. Next, Gould brought his pitch to the U.S. He was turned down by USA Today in December 2004, but five months later, after the craze had swept Europe, he landed it in the New York Post. USA Today began publishing its own Sudokus two months later. So far, Gould has made well over $1 million through his site.

Who is churning out all these puzzles?

London Guardian

Sudoku: The Hot New Puzzle Craze

What makes them so addictive?