According to international standards, the length of a credit card number is between 13 and 19 digits. The number of digits in each region is different.

Take China as an example. Generally speaking, most credit cards are 16 digits. Among them, digits 1-6 represent the credit card issuing bank, digits 7-12 are the serial number of the user's card, digit 13 can distinguish the primary card from the secondary card, digit 0 is the primary card, digits 1-9 are secondary cards, digit 14 It represents the time when the card statement was issued, the 15th digit represents the card number, and the 16th digit is the verification code.