As we discussed earlier this week, while credit card numbers look random, they actually have an internal coding scheme. Here’s a further breakdown.
Credit cards numbers are instance of ISO 7812 numbers, developed by the International Organization for Standardization in 1989 to regulate all magnetic strip id cards.
Every credit card number consists of the following:
Of note, the MII is considered part of the IIN. Also, an ISO 7812 number cannot be longer than 19 digits.
So, the next time you try to use your credit or debit card to enter an account number, be sure to leave off the first six digits and the last digit. — BEN POPKEN
ISO 7812 [Wikipedia]