You know sudoku, of course. Ever since the puzzle was introduced to the readers of The Times in 2004, it has taken the world by storm, and by now, sudoku are a staple in the daily puzzle section of newspapers, whether on- or offline.

20 years before that, sudoku had already been introduced to Japan by Nikoli, a publisher that specialises in logic puzzles and games. Over time, Nikoli has developed many different logic puzzles, a large part of which are language- and culture independent and can be attempted by anyone (you may need basic math skills though). In Japan, you can buy little books containing about 100 puzzles each, and despite everything being online these days, the books still appear popular.

One of Nikoli’s logic puzzles is called Fillomino, and this is how it is done: You start out with a rectangular grid, some of the squares containing numbers, others being empty. The goal is to create boundaries between contiguous regions, where each separate region containing the number n consists exactly of n squares; and two regions with the same number/size may not be adjacent and share a boundary (they may touch at a corner only).That means that a square containing the number 1 is its own region, two adjacent 2s lie inside the same region, etc.

Sounds easy? Well, caveat emptor: It is possible that two non-adjacent same numbers belong to the same region, and in the final result there may appear regions that had no numbers at the start.

Want to give it a try? Here is one of the hard puzzles I copied out of my current puzzle book – notice the sweating pencil? But we’re all nerds here, it shouldn’t be too big a problem for anyone of you… A hard fillomino to try out