Your 16 digit credit card number is not a random number. Each of the digits means something. I read about this today and am passing on what I learned.
The first digit is the industry of the credit card issuer. The first six digits are the ID of the issuer. Digits 7 through 15 are your account number. And the last digit is a checksum of sorts.
The checksum uses the Luhn algorithm. This is also called the mod 10 algorithm. It doesn't use any cryptography. It just tries to detect if any one of the digits is incorrect due to error.
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