It started as a puzzle challenge between an Australian husband and wife but now they are sharing their their modern twist on Sudoku -- and it's finding fans around the world.
Named Sudokion, the series of spacial logic puzzles take a Sudoku-style base and adds different colours, patterns and rules.
Michele Day said the game was originally a cheeky challenge from her husband Stephen Jones, whom she met at the University of Sydney Law School.
"It all stated when I took up Sudoku about six years ago which is kind of not my thing -- I’m not really a puzzles person,” Day said.
“It took Stephen a little bit by surprise and he had some time on his hands so he said ‘I could create a puzzle like this for you’.
“I did one of his puzzles and told him it was pretty easy, so he took up the challenge, creating more and more complex iterations."
Fast forward six months or so and he created one that was too hard for Day to complete.
"I couldn’t do it. He was delighted, not because I couldn’t finish it, but because he thought he might be onto something,” Day said.
Indeed they tentatively shared the puzzles with their daughter, who in turn shared them with a mathematical society newsletter and found others loved them too.
Next minute, they were being featured on mathematician Adam Spencer's radio show and being talked about in a Cambridge University newsletter.
Now they've set up a subscription-based website.
"The first time we really shared them, it felt like putting your youngest child on the stage," Day said.
"I was a little bit apprehensive. Now we've got a base of people doing the puzzles but it's very much in its early stages."
Day said they weren't all more difficult than traditional Sudoku.
"Of the range of puzzles we have, some are actually easier than Sudoku, they've just got added interest in the different ways in which you can solve them -- some are done very quickly right through to those that are much more complex and difficult to complete."
While traditional Sodoku requires players to place the numbers 1 to 10 on each row and column of a grid, Sudokion also requires additional number groupings within colours and patterns.
As for Day's journey from someone who wasn't really a puzzle person, through to a co-owner of Sudokion, she said she'd noticed regular brain teasers sharpened her brain.
"It does make you a bit more agile, you might be thinking along one line of reasoning and you see that you're not going to solve it that way. You need to think 'hang on a second, I need to change what I'm doing'.
"You need to think outside the square and come at it from a completely different angle.
"I think you can transfer that type of thinking to other aspects of life."
Play more Sudokion here.