The Mathematical Mysteries are a series of humorous thrillers with a slight mathematical tinge published by the very excellent Farrago Books. They are loosely connected, although each one can be read as a standalone adventure. I’d obviously advise starting at the beginning and reading right through to the end, because that way you’ll appreciate the overall story arc so much better. Also, I’ll make more money that way.
Look at these covers (by the brilliant Mark Swan aka kid-ethic), and tell me they’re not massively collectable. You can also click on them for more information about each book. If you’d like even more information, you might also like to dip into the amazingly comprehensive Archiepyedia, but I’d advise you to set aside an hour or two if you’re planning to do this. There are a number of rabbit holes to explore.
And as an added bonus, if you read these books you’ll get to find out what Vavasorology is all about. This will put you one up on this bunch, who really haven’t a clue, bless them: