Neil Sloane writes, "Run across a number sequence you want to identify? For instance, what comes next after 1, 2, 4, 9, 20, 48, 115, 286, 719, ...? The On-Line Encyclopedia of Integer Sequences is a database with over 50,000 such sequences. Serves as a "fingerprint file," so you can see if your problem has been studied before. Widely used by researchers in number theory, combinatorics, computer science, physics, chemistry, etc., as well as people trying to solve puzzles. " That's nuts. Mind you it would in no way have assisted me in getting a decent grade in calculus, but still, it's fun.