This episode mentions the number 42 as the Ultimate Answer to the Ultimate Question of Life, the Universe and Everything from 'The Hitchhiker's Guide to the Galaxy' by Douglas Adams.
This is a "ship in a bottle" episode - a term which dates back to Star Trek (1966), a series which this series often references. The entire episode takes place in a few constantly seen sets, to cut down on the budget for this "filler" episode.