How to Decode Credit Card Numbers

Yeah, there's nothing random at all about the number they issued you. Considering how many times people cancel a credit card number due to losing the card or suspected fraud, I'm surprised that they haven't had to add digits like crazy already. Warning: this video involves math, but you don't have to do it yourself. Just be impressed at the way computers can validate a credit card number in an instant. The video is only four minutes long, the rest is an ad. (via Boing Boing)