The Luhn algorithm—also known as the “Modulus 10 algorithm”—is a formula used to determine the accuracy of credit card numbers.

Luhn's Algorithm, also known as the "modulus 10" or "mod 10" algorithm, is a simple checksum formula used to validate a variety of identification numbers, most notably credit card numbers. The ...

The Luhn algorithm works as follows: Starting from the rightmost digit (excluding the check digit), every second digit is doubled. If doubling results in a number greater than 9, subtract 9 from it.

Obviously, with just a single check digit, not all errors can be detected (there’s a one in ten chance of a random number having the correct check digit), but the Luhn algorithm is clever in ...