Almost all credit card numbers used are generated using Luhn’s algorithm. Luhn’s algorithm is a simple checksum formula to validate variety of numbers. We can use the same formula for checking whether a given credit card number may be valid or not.

This can be used as a good technique to validate the credit card number in your web application. I found a simple function which validates any given number according to Luhn’s formula and gives the result to be true or false. The function is implemented in PHP and the primary source of this function is here.

<?php
function is_valid_luhn($number) {
  settype($number, 'string');
  $sumTable = array(
    array(0,1,2,3,4,5,6,7,8,9),
    array(0,2,4,6,8,1,3,5,7,9));
  $sum = 0;
  $flip = 0;
  for ($i = strlen($number) - 1; $i >= 0; $i--) {
    $sum += $sumTable[$flip++ & 0x1][$number[$i]];
  }
  return $sum % 10 === 0;
}

This small function is very useful if you want to check the validity of the credit card number being provided before passing it to your payment mechanism.

Sample Credit Card Numbers for testing

When I implemented this in my code, I also wanted to have some sample credit card numbers to test this. Sample credit card numbers are also very useful in many cases so here are the credit card numbers that I found.

Original Source for these numbers is this.

I have just tried to sum up all the info that helped me with credit card numbers in one post. I hope this saves some time for other people.