Asked by: Ian Morris, Ledbury
The Ancient Egyptians believed that 42 demons were present at the judgment of the soul; 42 is also a perfect score in the International Mathematics Olympiad. But in modern maths its main significance is the fun it provides by popping up in strange places. My favourite example is the sequence 42424242 that occurs 242,422 places after the decimal point in the number pi.
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.