My good friend Karl Erickson recently recommended a site called Project Euler (does not rhyme with "ruler") that promises endless fun. The site has hundreds of increasingly hard mathematical problems to solve. Most people solve them by writing and running a computer program that spits out the answer (although some do it with pencil and paper). You then plug your answer into the problem page (with a captcha). If you did everything right, you get a pat on the head. I solved Problem 1 in a few minutes with a 12-line Perl program and got a pat on the head in short order. It felt great. I can tell right away that this is going to be addictive. For the record, Problem 1 reads as follows:
If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.
Find the sum of all the multiples of 3 or 5 below 1000.
193,925 people have solved this now, including me. The next solver has just appeared. It says she took two hours to solve it, but maybe she's, like, 12. (Project Euler must be great for gifted kids.)
The latest problem, 368, is too long to reproduce here, but the title is "A Kempner-like series" and only 117 people have solved it.
I've started with Problem 1 and will move straight ahead as far as possible, until I lose my will to live and start subscribing to antinatalist newsletters. However, Karl says he sometimes skips around, and he has solved quite a few, so I may do the same if I'm really stuck.
By the way, this is a great way to exercise the skills outlined in the "Engineer Your Results" hack in Mindhacker.