Past the margins filled with complex geometric doodles, past the chunk of pages slipping from the cracked spine, past the hundreds of grids filled with blue and black digits, she flips to a clean sheet. She holds her red-ink ballpoint pen in her left hand, the point hovering just an inch from the page as she scans back and forth across rows and up and down columns. Then, with an intent gaze and confident motion, she stops at an empty box, drops the tip to the page and marks her first number.

With that crimson number six, Kerri Rainbolt, junior art history major, launches into another Sudoku puzzle, just one of hundreds she has tackled since becoming hooked more than a year ago.

In just two years, Sudoku has risen from a popular Japanese brainteaser to an international sensation. Each puzzle, about the size of a standard crossword, consists of a nine-by-nine grid of boxes.

The solution follows three simple rules: Each row, each column and each of the nine three-by-three sub-grids must each contain the digits one through nine. To find the only correct solution, players rely on a handful of clues, which are provided as numbers pre-printed in their proper squares.

For Rainbolt, the addiction began on a long car trip to Chicago with her father. She says she heard about Sudoku on television, so she picked up a book of puzzles at Target.

“I started out with the easy ones at first,” she says. “Now I can do hard ones, and it’s like nothing.”

Puzzles are rated as easy, medium and hard. Rainbolt says she can complete an easy one in two minutes and a hard one in 15 minutes.

“It’s so simple,” she says. “It’s just a bunch of numbers in a book in a grid pattern.”

She carries two well-worn Sudoku books in her bag and solves the puzzle in the Daily Kent Stater each day. For a while, she would solve four or five at night until she fell asleep.

Rainbolt says she gets a rush from the sense of accomplishment.

“I can do them,” she says. “I don’t have to think too hard at it.”

She doesn’t have any tricks, she says — just simple rules of deduction. Once she places a number in a row or column, it can’t appear anywhere else in that row or column.

For this puzzle, after filling in “sixes” where she can, she moves on to “twos,” then “ones.” She pauses, tilts her head to the side, then rapidly fills a row, then a column.

She floats the pen across the board, bobs her head, then begins filling in “threes” and “fives.” Another column, another row, another column. The puzzle is more than two-thirds solved.

By now she slows, moving more methodically. Square by square, she intently examines the grid. Then — suddenly — a revelation. Seven quick numbers, and she proclaims, “Ta da!”

Medium puzzle. Four minutes.

A Sudoku book in a Tokyo store inadvertently launched the current craze when it captured Wayne Gould’s attention in 1997. The 61-year-old New Zealand native, puzzle enthusiast and retired Hong Kong judge did not invent Sudoku, but he certainly manufactured today’s global infatuation.

“I immediately knew that I would enjoy it,” he says. “I bought the book of puzzles, and, indeed, I did. So I thought if I enjoyed it, other people would, too.”

Puzzles similar to Sudoku appeared in Paris in the 1890s, Gould says. Magazines published them in the 1970s, and by the 1990s Sudoku had acquired its Japanese name. But outside Japan, it was largely unknown.

So after his 1997 retirement, Gould spent six years developing a computer program that would randomly generate Sudoku puzzles. His computer skills were self-taught, but his family was certain what he was creating would be a winner.

“They were telling me as I was writing the program to hurry up because they thought it was great,” he says.

In 2004, the program was ready. He pitched one of its puzzles to a newspaper in New Hampshire, where his wife is a college professor. Shortly thereafter, he visited his daughter in England and pitched the idea to The Times, he says.

Both papers bought it.

In the two years since, Gould’s marketing push has created ardent Sudoku fans throughout the world. Puzzles generated by his computer program appear in more than 500 newspapers in 64 countries on six continents, he says. Gould offers the papers free puzzles for two reasons: first, because he’s a fan; second, to market his program.

“People wouldn’t buy a Sudoku program without knowledge of the puzzle,” he says.

The program, which he sells for $14.95 through his Web site, sudoku.com, generates a nearly indefinite number of new puzzles for users. Fans don’t need to worry about running out in their lifetime; the exact number of unique puzzles has been calculated as more than 6 sextillion — six followed by 21 zeros, he says.

Beyond the more than 50,000 unique visitors to his Web site each day, Gould has 16 to 18 books in print — “It’s a bit hard to keep count” — in 29 different languages.

Gould said he doesn’t know the number of aficionados worldwide.

“Anecdotally, it’s gotten pretty huge,” he says. “I think that I have only a small interest in the market right now.”

Of the hundreds of books on the market, only a few are his.

Still, he says, “I’ve done quite nicely.”

Gould says he was a world traveler even before Sudoku gave him global celebrity status among puzzle solvers. Now his fame has taken him to the World Sudoku Championships in Italy last March and to the Smithsonian Institution in Washington, D.C., for a Sudoku symposium in September.

It was a summer trip to New York City this year that created a Sudoku addict in freshman business major Winnie Wong. During hour-long subway rides from Brooklyn to Queens to visit her cousins each day, she watched Wall Street types, kids, women — nearly everyone — solving puzzles.

“It makes you look smart,” Wong says. “I think that’s why I started doing it.”

She, too, owns the books, but humbly declares she is not very good. When she buys a book, she tears the solutions out and throws them away so she can’t cheat.

She also visits counttonine.com, a Web site that tracks the time a user takes to solve a puzzle.

“I think my fastest was two minutes, but that was an easy one,” she says. “I don’t like to challenge myself too much.”

Wong’s method is deliberate. When she starts, she counts each number out loud.

Within a minute, her intensity builds. She stops speaking but jabs her pen at the page in a manner that implies the counts continue in her head. She scribbles numbers in the margins as placeholders, which she checks on occasion to aid her progress.

Hunched over the puzzle, she appears oblivious to chattering students who walk by. She counts to nine, stabs her pen, scratches a number — repeat.

With just five squares to go, she pauses, stuck. In a misstep, she writes the wrong number — a “one” — which she immediately corrects with a “six.” She sees an obvious digit in the center of the grid, and with three rapid-fire strokes, finishes the board.

Easy puzzle. Five minutes.

“It makes me giddy for 10 seconds, and then I want to do another one,” she says.

Wong says she finds it relaxing because it helps time pass quickly.

“I have no idea what just happened,” she says. “Sudoku eats brain cells.”

Brian Thornton is a graduate journalism student. This is his first story for The Burr.

Solve a Sudoku puzzle

Sudoku rules
1. Each row, column and three-by-three sub-grid contains only one each of digits one to nine.
2. Each puzzle has only one correct solution.

How to solve the puzzles
1. The object of the puzzle is to fill each empty cell with numbers one through nine.
2. The numbers already filled in are the clues you need to find the solution.
3. To figure out what number belongs in a cell, use the process of elimination.
Simply put: For any given cell, if a number already appears in that cell’s row,
column or sub-grid, it cannot also go in that cell.
4. When you think you know a number, write it in the cell.
5. Repeat this process of elimination until you have filled in all the cells.

Hints
1. Work in pencil to easily correct mistakes.
2. If you can narrow a cell down to two or three numbers, write those numbers in
the corners of the cell.
3. Don’t forget to look within rows, columns and sub-grids for the clues you need
to eliminate incorrect numbers.

—Brian Thornton