I found t his link that may help:
http://www.merriampark.com/anatomycc.htm
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Most Visa cards start with the number '4' and Mastercards with the number '5'.
5 = MasterCard 4 = VISA
Credit cards use 16 numbers with Mastercard starting with 5 an Visa with 4.
Credit card ID numbers have three (Discover, Visa, MasterCard) or four (American Express) digits.
The CV2 number is an additional layer of security added to Visa, MasterCard, and American Express credit cards for telephone and online purchases. The CV2 number for Visa and MasterCard credit cards is three numbers found on the back of the card. The CV2 on the American Express is four numbers found on the front of the card slightly above the credit card number.