The composition of the bank card number (usually 16 digits, some card types may be 13-19 digits) follows the international standard ISO/IEC 7812 and mainly consists of the following parts. The following takes the common 16-digit Visa card as an example to illustrate： --- ### **1. Main components** ####**(1) Issuing bank identification number (IIN/BIN)** -**The first 6 digits**: Assigned by the International card organization to identify the card issuer and card type. -*****: Start with `4` (such as`4***** `) -**Mastercard**: Start with `51-55' or `2221-2720` -**China Unionpay**: Starting with `62` *Example*: `423456` (assuming it is a bank's Visa card BIN). ####**(2) Personal account ID** -**7th~15th digits (9 digits in total)**: Assigned by the issuing bank to identify the cardholder's account. -The bank generates it according to internal rules and may contain information such as branch, product type, etc. -*Example*: `789012345' (fictitious account number). ####**(3) Parity bit (Luhn algorithm)** -**The last digit**: calculated by the **Luhn algorithm** and used for anti-counterfeiting verification. -*Calculation steps*： 1. From right to left, even digits×2 (if the result is ≥9, minus 9). 2. Add all the numbers together, and the sum should be a multiple of 10. 3. The parity bit is the number (0~9) that makes the sum meet the conditions. *Example*: Suppose the first 15 digits are `423456789012345`, and the check digit is calculated as `2` (full card number: `4234567890123452`). --- ### **2. Example of complete card number** -**Visa card**: `4234 5678 9012 3452` -Decomposition: `4` (Visa) + '23456`(BIN) + `789012345'(account) + `2`(check digit) -**Unionpay Card**: `6225 8812 3456 7890` -Decomposition: `62` (UnionPay) + '2588' (bank code) + '123456789' (account) + '0` (check digit) --- ### **3. Precautions for generating rules** -**Uniqueness**: The card numbers of the same bank are the same, but the account part needs to be unique. -**Security**: It is generated by an encryption algorithm when the actual card is issued to avoid continuous or predictable card numbers. -**Verification significance**: The Luhn algorithm can detect input errors (such as incorrect 1 digit or swapping adjacent digits), but cannot verify whether the card actually exists. --- ### **4. Important reminder** -**Protect privacy**: The real card number is sensitive information, do not disclose or try to generate another person's card number. -**Legal purpose**: This description is only used to understand the technical principles, and it is illegal to forge a card number. If you need to learn more about the specific rules of certain types of bank cards, you can provide the name of the card organization or bank, and I will add the details.