The first U.S. national sudoku tournament, featuring this year's world sudoku champion Thomas Snyder among the players, will be held Saturday at the Pennsylvania Convention Center.

The Philadelphia Inquirer Sudoku National Championship will be hosted by Will Shortz, the crossword editor at The New York Times.

More than 600 people, from teenagers to the elderly, had signed up for the number puzzle contest as of last week and more are expected to join on the opening day of the competition.

The top prize is $10,000 (euro7,067) and the winner will travel to the 2008 World Sudoku Championship in India as a member of the U.S. Sudoku Team.

The number of contestants comes close to the record number of crossword players -- 700 -- who competed at this year's American Crossword Puzzle Tournament in Stamford, Connecticut.

It is a remarkable feat considering that sudoku is a relatively young puzzle. Though it uses numbers, there is no math in sudoku. It consists of a grid of nine rows of nine boxes, which must be filled in so the numbers one through nine appear just once in each column, row and three-by-three square.

"The addictive thing about sudoku is after you get over the hump of the hardest part of the challenge of the puzzle, you fill in the last squares quickly and you feel a rush," Shortz said. "You immediately want to do another sudoku. I feel sudoku is a drug in that way."

Sudoku's origin can be traced to a game called Number Place, constructed by Howard Garnes and published in the late 1970s by Dell Puzzle Magazines.

A Japanese company called Nikoli Inc. brought it to Japan in the 1980s, where it became a hit. Then a New Zealander named Wayne Gould saw the game in Japan in the late 1990s, created a computer program to generate it and convinced The Times in London to carry it. It caught on in Britain and the U.S. craze began soon after The Conway Daily Sun in New Hampshire started printing sudoku puzzles in 2004.

Unlike crosswords, where players need a certain amount of knowledge to fill in the blanks, sudoku requires only a logical arranging of numbers -- hence its wide appeal.

"It's a broader spectrum of people solving sudoku," said Abby Taylor, editor-in-chief of Dell Puzzle Magazines. "For people who don't consider themselves puzzle people, this has sort of brought them into the fold."