The Secret Algorithm in Your Credit Card Number

Chances are you have a credit card in your wallet. On the front is usually your name, some other information like your bank and the card carrier like Visa, MasterCard, etc., and a string of 16, 15, 0r 14 digits. These digits vary from card to card and they're enough for merchants to transact business with your bank on your behalf. However, this string of numbers isn't random, in fact, there's a secret code in there that validates your card and keeps it safe, all in the number structure.

It's a low-tech mathematical algorithm called the Luhn Formula. Invented by Hans Peter Luhn in 1954, this mathematical tool actually dates back to before the existence of credit cards. Even with that fact, it's included in every credit, debit, and ATM card on earth – and it also makes for a mind-blowing bar trick if people don't know it.