There was originally a bug in the GAlib random number generator... if I remember correctly, the guy who identified it told me this was found (or demonstrated) by making a scatter plot of generated numbers an observing there was a pattern to the data.
Gridogram is a word game where the goal is to trace words in a letter grid to find a hidden quote. Behind the scenes, creating the letter grids for quotes is not obvious: the linked page describes the approach taken.
There's a bit of logic involved, a bit of maths with undirected graphs... hopefully it's of interest! Oh, and there's an interactive bit where you can try creating a grid for a quote, which in itself is kind of a fun challenge.