You credit card number may look like a random string of 16 digits that’s unique in the world but those digits reveal a little more than you think. For instance, the first digit of the card represents the category of industry which issued your credit card.
American Express is in the travel category and cards issued by them have 3 as the first digit. If you have VISA or MasterCard, your card’s first digit should be either 4 or 5 as they are from the banking and financial industry.
The first six digits of your credit card number identify the institution that issued the card to you. VISA cards follow the series 4xx while MasterCard uses 51-55 as the prefix.
You may even verify if a given credit card number is valid or not using simple addition. The following visual illustration courtesy of Mint.com will help you understand more about the anatomy of your credit card.