Credit Card
===========

On a credit card, a checksum is a single digit in the account number
that allows a computer, or anyone familiar with the formula involved, to
determine whether the number is valid. The checksum can help identify
credit card numbers that have been entered incorrectly – or phony credit
card numbers created by counterfeiters.

Foramt
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The format of a credit card number is as follows:

1. First 6 digits: Issuer Identification Number (IIN)
2. Next 9 digits: Account Identification Number (AIN)
3. Last digit: Checksum

Luhn Algorithm
--------------

The Luhn algorithm is a simple checksum formula used to validate a
variety of identification numbers, such as credit card numbers and other
documents. Use of the Luhn algorithm is a way to speed up the
verification process. The Luhn algorithm is particularly useful as more
transactions are performed online, where data breaches can be made
easily.

References
----------

-  `Wikipedia <https://en.wikipedia.org/wiki/Luhn_algorithm>`__
-  `Luhn-Algorithm <https://cleartax.in/g/terms/luhn-algorithm>`__