The vast majority of American Express credit card numbers start with 34, 37 and are 15-digit long, The credit card number must pass the Luhn Algorithm Check. Every American Express credit card has a specifically prefix like: 34 or 37.
|Credit Card Type||IIN ranges||Credit Card Number|
|American Express||34, 37||374313476701813|
|Discover||6011, 622126-622925, 644-649, 65||6011594786717005|
A Credit Card number must pass the Luhn Algorithm test to see if it is a valid credit card number.
The credit card number entered passed the Luhn Check so it is a valid credit card number!
The credit card number entered failed the Luhn Check. It's not valid?
Digits 7 to final number minus 1 indicate the individual account identifier (the last is the checksum).
The first six digits of a card number identify the institution that issued the card to the card holder.
The first digit of which is the Major Industry Identifier (MII), it indicates the individual account identifier.