http://en.wikipedia.org/wiki/Answer_to_Life,_the_Universe,_and_Everything

The Answer to Life, the Universe, and Everything is numeric in Douglas Adams’ series The Hitchhiker’s Guide to the Galaxy. In the story, a “simple answer” to The Ultimate Question is requested from the computer Deep Thought, specially built for this purpose. It takes Deep Thought 7½ million years to compute and check the answer, which turns out to be 42. Unfortunately, The Ultimate Question itself is unknown, suggesting on an allegorical level that it is more important to ask the right questions than to seek definite answers.