Know your number

What do credit card numbers mean and how are they generated?
Before we understand how credit card numbers are generated, here is a brief explanation of what a typical credit card number means.

Out of the 16 numbers on a typical credit card, the set of first 6 digits is known as the issuer identifier number. The last digit, known as the “check digit”, is generated in such a way as to satisfy a certain condition (the Luhn check). The term sounds intimidating, but it’s really a very simple (and elegant) concept.

Taking away the 6 identifier digits and the check digit leaves us with 9 digits in the middle that form the “account number”.
There are 10 possible numbers (from 0 to 9) that can be arranged in these 9 places. This gives rise to 1 billion possible account numbers (per issuer identifier).

With each account number, there is always an unique check digit associated (for a given issuer identifier and an account number, there cannot be more than one correct check digit)