42: Happy 30th, Hitchhikers' Guide
Theories abound, from hidden Lewis Carroll references to the average number of lines on a paperback. Actor Stephen Fry (the voice of the audio books)claims to know the truth. Personally, I think it's just a random number: answering such a big question with a simple integer is meant to be a joke, but it's become something much more in the eyes of HHGG fans.
It's 30 years since Douglas Adams' The Hitchhiker's Guide to the Galaxy made its debut on BBC radio, but its most famous mystery is still waiting to be resolved.
The radio series - which subsequently became both bestselling book, television series and film - traces the travels around the galaxy of Arthur Dent, after the earth is destroyed to make way for a "hyperspatial express route".
Possibly the most famous line in the whole book is the "answer to life, the universe, and everything" given by the supercomputer, Deep Thought.
A BBC radio script based on Adams' book contains the following lines:
("Cave man" lays out following sentence in Scrabble stones: "What do you get if you multiply six by nine?")
Arthur: Six by nine? Forty-two? You know, I've always felt that there was something fundamentally wrong with the Universe.
(Faint and distant voice:) Base thirteen!
It sparked Adams' retort: "I don't write jokes in base 13."