And the national obsession is now going global as Rupert Murdoch-owned publications lend a hand in spreading the phenomenon from The Times in London to the New York Post and now to Murdoch's Australian journals.
The addictive puzzle's first major U.K. appearance was in The Times last November. Every newspaper has since launched its own version, flagging up su doku on the masthead to harness its popularity and sell newspapers.
Su doku books are even outselling "The Da Vinci Code" as the nation embraces this brainteaser from the Far East. Su Doku presents a grid of 81 squares divided into nine blocks of nine. Some squares contain figures and the goal is to fill in the empty squares so that the numbers one to nine appear in each row, column and block.
The puzzle's popularity lies in the fact that it's all about logic and patience. "Anyone can do it. You just need to be able to count to nine," said Tim Preston, publishing director of Puzzle Media. "It's not about maths-the numbers could be symbols or the names of people you've dated."
Its origins are unknown, but versions have been found in ancient China and the current craze was generated by Wayne Gould, a New Zealand judge who picked up a su doku (roughly translated as "unique number"), in Tokyo and was so gripped that he spent the next six years developing a computer program to generate the puzzles.
Passing through the U.K. he stopped off at The Times' offices and sold the concept to Features Editor Mike Harvey. "I tried to send one of my staff to shoo him away," said Mr. Harvey, "but they told me to do it myself. When I got to reception he had very smartly faked up a back page of The Times with a su doku on it.
"It took me two minutes to say yes. It was simple to understand how it works and how to play. It has a depth of logical complexity and Times readers like having their wits tested. Within a few days it was obvious that readers thought it was a great thing so we put out a book."
Competition to maintain readers' interest is fierce. The Times has been at the forefront of su doku innovation, releasing a cellphone version that costs $9 to download 10 puzzles. The grid appears on the phone's screen and players complete the puzzle by navigating around the handset and its numbers.
The Guardian's unique selling point is that its puzzles are created by individuals, not computer programs. Mr. Preston, who supplies The Guardian's puzzles, said, "It gives you the satisfaction that you are pitting your wits against an individual who has thought about what your next step would be and has tried to obscure the path."
The Guardian, which was fifth to market, launched its su doku with a special edition featuring a puzzle on every page. The Sun's version is called "Sun Doku" and the Independent has developed a national su doku event in which contestants will compete for the title of U.K. Grand Master.
The Times and The Telegraph have published dedicated books, while The Telegraph has produced a challenging 3D version. German publisher Bauer and Puzzler Media have both launched monthly publications dedicated to su doku. Even BBC Radio 4 has got in on the act, reading out numbers to listeners.
"I have worked in puzzle publishing for 20 years and I've never seen anything like it," said Mr. Preston. "We sell 17 million publications a year and almost none contain any puzzle to do with numbers because they are never popular. It's peculiar. I can't explain it except to say that the newspapers are responsible for lots of the hype because of their rush to outdo each other."
But does su doku sell issues? While Puzzler's first issue sold out in two weeks and the second is selling just as fast, it's harder to determine how newspaper sales are affected. No self-respecting publication would admit that a puzzle outweighs its journalism as a reason to buy, but there is anecdotal evidence that su doku increases loyalty and purchases.
Michael Mepham, puzzle compiler at the Daily Telegraph, has received e-mail from readers who have scoured foreign cities in search of a copy of the Telegraph, desperate to do that day's puzzle. He also received more than 60,000 e-mails in one week from dedicated enthusiasts. "There are a lot of su doku nerds out there," he said.
Janine Gibson, an editor at The Guardian, said that when her newspaper launched its own so doku, she had plenty of feedback from readers saying, "Thank God they didn't have to buy The Telegraph or The Times on top of their Guardian purchase."
"It's difficult to say how many more copies su doku sells because our circulation is up since we went tabloid, but anecdotally there is no doubt it sells," said Mr. Harvey.
Spike Figgett, publishing director of Bauer, said su doku "appeals to a demographic who aren't normally that interested in puzzles. It's a mix between men and women, between mid-market and broadsheet readers."
And then there's the money to be made from su doku. Or is there? Wayne Gould now sells puzzles around the world, but Mr. Harvey said he doesn't make a lot of money out of it. "He didn't go into this to make money. He thought it was a great puzzle and wanted more people to do it."
Mr. Mepham receives royalties from his books and from syndication of his puzzles, created by his own modified computer program, around the world. He is supplying publications in Australia (that he can't yet name) and will soon be supplying the Los Angeles Times. He is so busy that he regularly misses whole nights of sleep.
Nikoli, the Japanese company that supplies Puzzle Media and invented the name su doku, is seeing demand and profits soar. There is a back catalog of 20 years' work to plunder if its puzzle compilers can't keep up with the demand.
The company does not believe in pushing its valued employees too hard. In a reverse of the traditional Japanese work ethic, Nikoli believes that if its employees don't have fun working, then its customers won't have fun doing their puzzles. So staff work short hours and are regularly sent on golfing trips to beautiful locations.
Despite su doku's success, its commercial potential remains under-exploited. The newspapers do not have sponsors for their puzzles despite obvious synergies with some brands. Cereal marketers may also be missing a trick-they could carry the puzzles on their packaging, encouraging loyalty and providing entertainment at the same time.
"It would be useful as a marketing tool," pondered Mr. Mepham. "You could incorporate telephone numbers into the grid. It gets people to concentrate and stare at a page for 15-20 minutes, but it's still so immature in this country-it's only really taken off in the last five or six weeks."
At least this way, if the craze dies out as quickly as it started, su doku could quietly disappear from print and nobody would get hurt. Ms. Gibson acknowledges, "It can't possibly enjoy this level of exposure forever. The stampede has been too quick. It's too soon to know if it will stick around."
But su doku has been around for thousands of years, in various guises. A similar game, called Number Place, ran in Dell Puzzle Magazine in New York in the 1970s. In 1783 a blind Swiss mathematician devised another prototype called "Latin squares."
There is no doubt that the name su doku, which hints at the mysticism and appeal of the Land of the Rising Sun, has helped propel the puzzle to its current success.
"It's a short-term opportunity that I hope will still be here in the medium to long term," Bauer's Mr. Figgett said. "A lot of people demand a daily dose."
Doubters have dubbed su doku the Rubik's Cube for the 21st century. But as Mr. Mepham said, "It's been popular all through history. It's always been around and now in the information age we can distribute it well. I believe it will run and run."
Why you care
It’s headed here next and consumers love it
It’s proving a good tool to boost book and newspaper sales
It could be employed as a promotions tool. Cereal boxes anyone?