You are powerless to stop KenKen. Perhaps the new Japanese arithmo-logical challenge, which debuted in the New York Times on Feb. 8, will burrow into your brain on account of a significant other, who will plead for your help as she softly coos the game's tantalizingly simple rules. Or maybe a boring subway ride will leave you staring at a discarded newspaper, from which an unsolved KenKen will silently beckon your understimulated brain. However it goes down, don't try to resist. The marketing wheels, greased by the promise of Sudoku-style riches, are already in motion. New York Times puzzle maven Will Shortz calls it "the most addictive puzzle since Sudoku." He'd better hope so, as Shortz has already put out a slew of books of this computer-generated brain-mangler, with titles like Will Shortz Presents KenKen Easy to Hard Volume 3, Will Shortz Presents: I Can KenKen! Volume 1, and Will Shortz Presents the Little Gift Book of KenKen.
What exactly is this new creature? Like Sudoku, KenKen is a simple game whose rules can be expressed in a couple of bullet points:
- Fill the grid with digits so that no digit is repeated in a row or column. In a 4-by-4 grid, you'll need to use the digits 1, 2, 3, and 4 in each row and column. In a 5-by-5 grid, you'll use 1, 2, 3, 4, and 5—and so on as the size of the grid increases.
- Within each outlined set of boxes—these sets are called "cages"—use the given arithmetical operation to arrive at the number indicated.
Here's a sample grid:
Take a look at the two-box cage in the upper-right of the diagram. Your goal is to place two digits in this cage such that the difference between them is 1. You can subtract either backward or forward—if you want to use the digits 1 and 2, it's valid to put the 2 to the left of the 1 or the 1 to the left of the 2. In the three-box cage below it, you need to multiply three digits to get 60. Since this is a 5-by-5 puzzle, there is only one potential combination that will work: 5, 4, and 3. It's up to you to figure out what order the digits need to go in for the puzzle to be solved correctly. (To see the solution, click here.)
KenKen—tip for wannabe puzzle-craze instigators: the name was cleverly trademarked by its promoters to discourage too-blatant imitators—does share some features with Sudoku. Both demand high-powered deductive reasoning skills from solvers, for example. The big difference between the two is that Sudoku has nothing to do with math—you can play with symbols rather than numbers—while KenKen requires some degree of arithmetic skill, especially with larger puzzles. If you're solving a 9-by-9 grid, you may be required to multiply, say, 7 by 5 by 9 by 3 in your head. If the KenKen people are smart, they'll market a branded set of calculators for the mathematically impaired.
Though KenKen is a fun game, even mesmerizing at times, it's by no means unique. Ever since Sudoku landed on American shores in 2005, puzzle writers (me included) have been trying to come up with the Next Big Japanese Logic Puzzle Craze, with mixed results. Kakuro, a math-cum-logic puzzle closer to KenKen than Sudoku, didn't make quite make the second-wave splash that puzzle-book publishers had hoped for in 2006. That same year, I tried singlehandedly to create the third wave with a word-logic hybrid called Kaidoku, but it turns out I don't (yet!) possess the Shortz-ian clout to tell America which puzzle it will be solving this year. (I also didn't trademark the name Kaidoku, which turned out not to matter, since no imitators followed.)
Why do some puzzles take off and others don't? As a puzzle writer, I wish I knew. Group psychology in puzzle trends is more art than science, as it is with music, movie, and food trends. Some ever-shifting combination of tastemakers, timing, and Gladwell-ian tipping points is involved, but no one knows the precise mix. Sudoku took off because it massages the brain in a way that crosswords don't, and its marketing was extremely clever—its main popularizer, a New Zealander named Wayne Gould, syndicated the puzzle to newspapers for free as a means to sell his Sudoku-writing computer program. Ensuing copycat puzzles—the Kakuros and Kaidokus—haven't done as well because they're not that different from that other game with the grid and the numbers. Sudoku got there first, so that part of people's brains has already been massaged.
So, what to make of KenKen? While I'm confident that you won't be able to resist its charms the first or second time, no one knows whether it will stand up to repeated play over weeks, months, or years. If anyone can start a puzzle craze, it's Shortz, but book sales are middling so far, and Shortz's very entertaining YouTube video explaining the game has an OK-but-not-through-the-roof 30,000 views. The shrinking newspaper market is also much less fertile ground for a new puzzle than it was in 2005, and it was newspaper syndication that facilitated the Sudoku explosion. (KenKen does appear in a couple of dozen papers already.)
Only time and the puzzle-solving public will determine KenKen's fate. The puzzle's marketers—a team that includes Shortz—are wisely playing up the Japanese angle of the puzzle. Unlike Sudoku, popularized as a Japanese puzzle craze though invented in the 1970s by an architect from Indiana, KenKen really was created by an Asian fellow, a Tokyoite math teacher named Tetsuya Miyamoto. We Americans tend to go for Japanese fads and trends (think Hello Kitty, karaoke, and Pokémon), so the product's exotic name and origins can't hurt. (Sudoku languished in obscurity for decades in American puzzle magazines, tagged with the unsexy name Number Place.)
So, should you KenKen? Sure, why not? I'm not above participating in (or even starting) a top-down, inorganic puzzle craze. Try the puzzles in the Times or elsewhere, and if you like them, which you probably will, then buy a book or two. I'll probably pick up (and perhaps publish) a volume myself. But remember that KenKen isn't the only number puzzle in the sea. If you enjoy the Times' new puzzle, consider buying the magazine GAMES World of Puzzles the next time you're in the grocery store. It costs less than a book of KenKen, and it's filled with dozens of different types of puzzles—word, logic, math, visual, the whole gamut. You may even like some of them better than KenKen. If you're feeling entrepreneurial, you could always take a shot at slapping a Japanese name on one of them and marketing it to the masses. Kendoku, anyone?