4 - the first digit is the Major Industry Identifier.It designates the category of the entity which issued the card.
1 and 2 are airlines
3 is Travel and Entertainment
4 and 5 are Banking and Financial
6 is Merchandizing and Banking
7 is Petroleum
8 is Telecommunications
9 is National assignment
The first 6 digits are the Issuer Identification Number. It will indentify the institution that issued the card.
Visa: 4xxxxx
Mastercard: 51xxxx - 55xxxx
Discover:6011xx, 644xxx, 65xxxx
Amex: 34xxxx, 37xxxx
Cards can be looked up by their IIN.
A card that starts with 376211 is a Singapore Airlines Krisflyer
American Express Gold Card.
529962 designates a pre-paid Much-Music MasterCard.
The 7th and following digits, excluding the final digit, are the person`s account number. This leaves a trillion possible combinations if the maximum of 12 digits is used. Many cards only use 9 digits.
3 The final digit is the check digit or checksum. It is used to validate the credit card number using the Luhn algorithm
How to validate a credit card :
Take the above number (or any credit card number)
4417 1234 5678 9113 (And double every other digit from the right)
*2 *2 *2 *2 *2 *2 *2 *2
----------------------------
8 2 2 6 10 14 18 2
Add these new digits to undoubled ones
4 7 2 4 6 8 1 3
All double digit numbers are added as a sum of their digits,so 14 becomes 1 + 4
8+4+2+7 + 2+2+6+4 + 1+0+6+1+4+8 + 1+8+1+2+3
=70
If the final sum is divisible by 10,then the credit card number is valid.
If it`s not divisible by 10,the number is invalid or fake.Try it and see.
