The rules for generating bank account numbers and the methods for identifying authenticity vary from country to country and region. The following are some common international rules and descriptions of bank accounts in mainland China (take Unionpay card as an example).： --- ###**1. Bank account number generation rules** #### **1. International bank account number (IBAN)** -**Structure **: Country code (2 letters) + verification code (2 digits) + bank identification code (SWIFT/BIC) + branch code + account number. -**Verification rules**： -Convert letters in IBAN to numbers (A=10, B=11. . . Z=35). -Treat the entire string as a large integer and calculate the remainder divided by 97. If the result is 1, it is valid. #### **2. Mainland China Unionpay Card (19 digits)** -**Structure**： -The first 6 digits: the identity of the issuing bank (such as Industrial and Commercial Bank of China: 622202). -Middle 6-13 digits: customize the issuing branch (region, branch, account type, etc.). -Last 1 digit: Luhn algorithm check code. -**Generation rules**： -The top 6 positions are allocated by the People's Bank of China. -The check code is calculated by the **Luhn algorithm** (see below). #### **3. US account (Routing Number + Account Number)** -**Routing Number (Routing Number)**: 9 digits, the first 4 digits are the Federal Reserve Bank code, the last 4 digits are the bank code, and the last 1 digit is the check code. -**Account number**: Customized by the bank, may contain check digits. --- ###**2. Authenticity identification method** #### **1. Check code algorithm** -**Luhn algorithm** (used for UnionPay cards, credit cards, etc.)： 1. From right to left, even digits are multiplied by 2 (if the result is ≥10, split and add). 2. All numbers are added together, and the sum should be a multiple of 10. *Example*: The last digit `1` of the card number `6222021234567891' is the check code. -**IBAN verification**： Use the international standard modulo 97 algorithm to verify whether the check code is valid. #### **2. Official tool verification** -**Banking system query**: Verify the existence of the account through the bank counter, online banking or API interface. -**Third-party tools**: such as IBAN verifier (you need to ensure the authority of the tool). #### **3. Format check** -**Length**: China Unionpay cards are 19 digits, and the length of IBAN varies from country to country (such as 22 digits in Germany and 27 digits in France). -**Prefix matching**: Check whether the issuing bank code is consistent with the bank's public information (for example, China Merchants Bank starts with `6225`). --- ###**Three, precautions** 1. **Do not rely only on algorithms**: The verification code can only verify whether the number complies with the rules, and cannot confirm whether the account really exists. 2. **Privacy and law**: It is forbidden to use other people's real accounts for testing to avoid violating the law. 3. **Dynamic changes**: Some banks may adjust their rules, subject to the latest official information. If you need to verify the authenticity of your account, it is recommended to go through the official bank channels (such as small verification before the transfer) or contact a financial institution.