Perfectly pure happiness:

"The answer to this is very simple. It was a joke. It had to be a number, an ordinary, smallish number, and I chose that one. Binary representations, base thirteen, Tibetan monks are all complete nonsense. I sat at my desk, stared into the garden and thought '42 will do' I typed it out. End of story." from the man himself[1]

...but let us not ruin a good story with the truth. Remember why earth was built. The "real" answer might then be flowing in the ether.

[1] https://en.wikipedia.org/wiki/Phrases_from_The_Hitchhiker%27...

I think it was intentional but I don't have a source.

Edit: from the other comment, it appears it was in fact random...