On Fri, Apr 27, 2007 at 08:59:49PM +0900, Ruby Quiz wrote:
> The first check people often do is to validate that the card matches a known
> pattern from one of the accepted card providers.  Some of these patterns are:
> 
> 	+============+=============+===============+
> 	| Card Type  | Begins With | Number Length |
> 	+============+=============+===============+
> 	| AMEX       | 34 or 37    | 15            |
> 	+------------+-------------+---------------+
> 	| Discover   | 6011        | 16            |
> 	+------------+-------------+---------------+
> 	| MasterCard | 51-55       | 16            |
> 	+------------+-------------+---------------+
> 	| Visa       | 4           | 13 or 16      |
> 	+------------+-------------+---------------+

Wikipedia has a great chart showing all the prefixes of most known
credit cards, along with lengths and overlap between cards (currently
none).

http://en.wikipedia.org/wiki/Credit_card_number

enjoy,

-jeremy

-- 
========================================================================
 Jeremy Hinegardner                              jeremy / hinegardner.org