THHGTTG/42

42 is the answer to Life, the Universe and Everything, as given by a supercomputer to a group of mice in Douglas Adams's The Hitch Hikers Guide to the Galaxy.

The question to which 42 is the answer is not fully known. One of the theories is that the question is "What is 6 times 9?" This theory only works if the calculations are done in base 13 (not base 10.)