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The
numbers found on credit cards have a certain
amount of internal structure, and share a common
numbering scheme.
The
card number's prefix, called the
Bank Identification Number,
is the sequence of digits at the beginning of the
number that determine the bank to which a credit
card number belongs. This is the first six digits
for Mastercard and Visa cards. The next nine
digits are the individual account number, and the
final digit is a validity check code.
In
addition to the main credit card number, credit
cards also carry issue and expiration dates (given
to the nearest month), as well as extra codes such
as issue numbers and
security codes.
Not all credit cards have the same sets of extra
codes nor do they use the same number of digits.
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