title: Can Credit Card Numbers contain leading zeros?
body: <p>Often I have stored credit card numbers in <code>varchar(16)</code>. That works, but it takes 17 bytes per number.</p>
  
  <p>Storage is not that big a deal, but I like to be efficient, for both storage requirement, and table search time.</p>
  
  <p>If I could use <code>decimal(16) unsigned</code>, I could cut the storage requirement to 7 or 8 bytes, and still preserve readability as well as much of the compatibility.</p>
  
  <p>This would strip leading zeros. Can I depend on all credit card numbers starting with a non-zero number?</p>