Almost five years after The Times introduced Su Doku to the puzzle-loving public, the ever-expanding brain teaser continues to defy expectations as easily as its more fiendish variants defy the best logicians.

A Sunday newspaper announced in March this year that Su Doku had been solved — by the devising of a formula that would solve any variant of the puzzle, no matter how difficult. An American computer scientist was going to unveil “a pen and paper algorithm” for cracking the puzzles in five logical steps.

Sorry, but we’ve been here before. When The Times launched Su Doku on November 12, 2004, it received a letter a few days later from a correspondent saying that he had devised a computer program to solve the puzzle.

So is it game over? Not quite. You see, the history of Su Doku has been punctuated by regular claims to have solved it or cracked it or beaten it. They all miss the point. Su Doku fans don’t want to switch on a computer to crack the fiendish or super-fiendish puzzles. As one disgruntled reader put it, in response to the Sunday newspaper claims this year: “This is nonsense . . . the fun is solving it with your brain.”

Tom Collyer, The Times National Su Doku champion in 2007, criticised the supposed magic formula as stating the obvious: “[It] describes a few techniques contained in the preface of countless Su Doku books — before then describing a guessing process. The conclusion? If you make enough guesses, you’ll get the answer. Amazing!”

The really amazing thing about Su Doku is how indispensable it has become to millions of people across the world since its populariser in its modern form, Maki Kaji, published it in Japan in 1984 (Kaji based his puzzle on a game called Numbers in Place that appeared in a US magazine). Su Doku now appears in more than 600 newspapers, thousands of websites and dozens of books in at least 70 countries. There are Su Doku television games, mobile phone games, video console games and, most recently, about 30 games for the iPhone.

The Times has developed its original Su Dokus into increasing levels of difficulty, and offers readers Killers, Samurai Su Doku and, since last Christmas, the three-dimensional Tredoku on Saturdays. Our website, timesonline.co.uk, launched an interactive Su Doku in March that has rapidly become one of its biggest hits. Our market research shows that Su Doku is the most popular puzzle in the newspaper, having overtaken our famous crossword, among game-playing readers.

So, as we launch this year’s Times National Su Doku Championship with a week of special qualifying puzzles, Su Doku remains unchallenged in its popularity for all kinds of reasons — and not always logical ones. One reader complained (or was it praised?) the puzzle five days after its inception, saying that her husband would not speak in the morning until he had done it (and the crossword and Polygon and Word Watching).

So, try the puzzles in The Times this week and see if you can be our 2009 champion.

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