Ye' old general discussion board. Basically, for everything that isn't covered elsewhere. Come here to shoot the breeze, shoot your mouth off, or whatever suits your fancy. This forum is not for asking programming related questions.
As with most good magic tricks there are a couple things going on that combined that make it work. The basic math of the thing is the foundation, but then they use unusual, unmemorable symbols and rearrange them every time that the page is displayed. That way you can do it several times and get a different symbol -- even though the answers are in the same positions.