At least, that's the answer given in The Hitchhiker's Guide to the Galaxy. This immediately brings up the issue: what was the question? In the book, it turns out the Earth is a massive computer program that is set to output the question after a running time of 5 billion years. But unfortunately it is accidentally destroyed a few days before terminating the program by a careless alien species making room for an interstellar highway system.

Perhaps the question is "What is the derivative of 42x?"