Has sudoku got your number?

Humans seem to have an innate desire to fill in empty spaces. Perhaps that is part of the appeal of sudoku--the new international puzzle craze. The object is to fill in a grid with numbers so that every row, every column, and every 3-by-3 box contains the digits 1 to 9 without repeating. There is no math involved. In Japan, the puzzles have become as popular as crosswords are in the U.S. Sudoku spread to the West in November 2004, when Wayne Gould, a retired judge in London, persuaded The Times of London to print a sudoku puzzle. Gould had seen sudoku in a Japanese magazine and developed a computer program for creating the puzzles. Since April 2005, when the New York Post introduced sudoku in the U.S., more than half of America's leading newspapers have begun printing one or more of the puzzles each day. Nearly all sudoku are generated by computer programs that understand the solving strategies and determine the difficulty of the puzzles. And sudoku fans don't need to worry about the puzzles running out: The number of possible ways to fill a 9-by-9 sudoku grid is calculated at 6,670,903,752,021,072,936,960.