Answer to Life, the Universe, and Everything

Forty two?!" yelled Loonquawl. "Is that all you've got to show for seven and a half million years' work?"

"I checked it very thoroughly," said the computer, "and that quite definitely is the answer. I think the problem, to be quite honest with you, is that you've never actually known what the question is."

It takes Deep Thought 7½ million years to compute and check The Answer, which turns out to be 42. Unfortunately, The Ultimate Question itself had long been forgotten.