All mainstream credit card numbers obey a mathematical trick designed to catch the most common typos. It’s called the Luhn ...

Credit card numbers aren't random, and they don't only identify your account. Here's how to decipher what your own credit card number means.

The Luhn algorithm uses modulo-10 mathematics. To calculate the check digit, multiply every even-position digit (when counted from the right) in the number by two.

If the result is not a multiple of 10, then the credit card number is invalid. I’ll show the Luhn algorithm in action on my Visa, but you should try it with your credit card, too.