title: Does the Luhn algorithm work for all mainstream credit cards? (Discover, Visa, Mastercard, Amex)
body: <p>Reference: <a href="http://en.wikipedia.org/wiki/Luhn_algorithm">Luhn Algorithm</a></p>
  
  <p>The Luhn Algorithm is a great way to quickly verify that the user typed their CC # in correctly.</p>
  
  <p>However, I am concerned that there may be a subset of mainstream credit cards that do not use Luhn-Algorithm-friendly numbers.</p>
  
  <p>I do have logging in place in our application to detect a pattern in all Luhn-Algorithm-rejections, but I'd rather know definitively. </p>