I wrote code for this ten or so years ago. I don't say that to brag, but to express my annoyance at every credit card form I encounter on the internet. Why do you ask me for my number <i>and</i> what type of card I've got?
This is a bad submission: it's trivial to get this info. Flagging. Sorry I'm also posting this comment. Top hit for "credit card number format" has all this info. <a href="http://www.merriampark.com/anatomycc.htm" rel="nofollow">http://www.merriampark.com/anatomycc.htm</a>