Try this at home, its fun:

From the September 13, 2007 edition of The Economist. Algorithms
Business by numbers

People often make mistakes when they key in their credit-card numbers online. With millions of transactions being processed at a time, a rapid way to weed out invalid numbers helps to keep processing times down. Enter the Luhn algorithm (see [above] ), named after its inventor, Hans Luhn, an IBM researcher. The numbers on a credit card identify the card type, the issuer and the user's account number. The last number of all is set to ensure that the Luhn algorithm produces a figure divisible by ten. If it is, the card number has been properly entered and the processing can go ahead.

Cool Link

Want to send a railroad car of corn from Omaha to Chicago? See how much it will cost using Union Pacific's price guide.

Put in the route, the type of product being shipped, the type of railcar to ship the product and out comes the price.

Usually a combination of a flat rate and a fuel surcharge. Shipping by rail is so much more efficient than by truck.

http://c02.my.uprr.com/cdm/price_query.jas

With higher fuel prices, this bodes well for rail companies. Investors, like Warren Buffett have really driven up shares of railroad stocks in the last couple of years.