A Sudoku Secret Pattern in Plain Sight

Solving Sudoku puzzles has become a very popular pastime around the world since the Times of London began publishing them twenty years ago. Although the puzzle itself has been around for much longer, it was its appearance in the Times that prompted its popularity to explode.

The puzzle itself can be described as a kind of simplified crossword puzzle, but with numbers. And maybe not so simple. Sudoku.com sets out the basic rules:

Sudoku is played on a grid of 9 x 9 spaces. Within the rows and columns are 9 “squares” (made up of 3 x 3 spaces). Each row, column and square (9 spaces each) needs to be filled out with the numbers 1-9, without repeating any numbers within the row, column or square.

Sounds simple, right? In practice, how simple a Sudoku puzzle is to solve depends on how many numbers have already been filled in on it. Here’s an example of a moderate-to-easy-to solve Sudoku puzzle you can try on your own.

In solving this puzzle, you’re taking advantage of Sudoku’s rules to fill in the missing numbers. Since each number from 1 to 9 can only appear once in each row and column, and only once in each 3 x 3 box, you can use a process of elimination to identify where the correct digits to solve the puzzle can be placed. For instance, you can probably find the right place to insert a number 9 pretty quickly just by looking at the left-most column, the bottom two rows, and the upper-left 3 x 3 box.

Like crossword puzzles, Sukoku puzzles also have a kind of symmetry to them. It’s that symmetry, combined with Sukoku’s rules, that offers a way to find the right places to put the missing numbers. You just have to see the secret pattern and that’s what the following Numberphile video featring Cracking the Cryptic’s Simon Anthony is all about:

Now that you know about the Phistomephel Ring, as this secret pattern hidden in plain sight is called, try using that knowledge to help solve your next Sudoku puzzle.

Image credit: Sudoku Puzzle by L2G-20050714 standardized layout on Wikimedia Commons. Creative Commons CC0 1.0 Universal Public Domain Dedication.