Numb3rs Fanfic Finders

I'm looking for fics that have Charlie solving riddles/puzzles using math. I don't mean like using math to catch the latest bad guy, but answering questions/solving puzzles like he did in Janus List.
Anybody get what I'm trying (rather unsuccessfully me thinks) to say here?

Help would be greatly appreciated.
Gen and slash (Don/Charlie)is fine.