The information provided below is limited to basic principles and examples in the public domain. It does not involve the actual internal algorithms of any bank or financial institution, nor should it be used for any illegal purposes. It is only for academic and theoretical research reference. ──────────────────────────────── 1. Different banks and countries may have their own rules about the composition of bank account numbers, but generally bank account numbers will contain the following parts: a. A code that identifies the institution or branch (such as bank code, branch number, etc.); b. A customer-specific serial number or account identifier; c. A check digit, which is used to detect input errors and is usually calculated using modular operations (such as mod 10, mod 11, or Luhn algorithm). For example, in some countries, the account numbers of large banks may use a fixed-length structure: the first few digits are the bank and branch code, the middle is the customer number, and the last digit is the check digit. ──────────────────────────────── 2. A common check digit calculation example (based on weighted sum and then modulo, similar to mod 10 or Luhn algorithm) Suppose we design a simple account number rule, the rule is as follows: a. The account number has 12 digits, of which the first 11 digits are the main digits and the last digit is the check digit. b. Check digit calculation method: multiply the first 11 digits according to the predetermined weights and sum them, then take the sum modulo 10, and the remainder is the check digit. Example description: Assume that the account entity is: D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 The preset weight sequence is: w1, w2, …, w11 (for example, it may be [1, 3, 7, 1, 3, 7, 1, 3, 7, 1, 3]) Calculation steps: 1. Calculate S = w1×D1 + w2×D2 + … + w11×D11 2. Check digit D12 = S mod 10 3. The final account number is D1 D2 … D11 D12 For example: Assume that the entity number is 12345678901, and the weights are [1,3,7,1,3,7,1,3,7,1,3], then calculate: S = 1×1 + 3×2 + 7×3 + 1×4 + 3×5 + 7×6 + 1×7 + 3×8 + 7×9 + 1×0 + 3×1 = 1 + 6 + 21 + 4 + 15 + 42 + 7 + 24 + 63 + 0 + 3 = 186 Check digit = 186 mod 10 = 6 The final account number is 123456789016 This method is just an example. In practice, banks may adopt more complex weight distribution, modulus or other variant algorithms to ensure the strictness of the verification and anti-counterfeiting requirements. ──────────────────────────────── 3. Example of the structure of International Bank Account Number (IBAN) IBAN (International Bank Account Number) is an international standard format. Many European and other countries use this format. Its composition generally includes: a. The first two digits: country code (for example, "CN" represents China or other country code) b. The next two digits: check digit. These two digits are generated by a specific algorithm based on the entire number c. Subsequent part: Basic Bank Account Number (BBAN). The structure is determined by each country For example, assuming that the IBAN format of a certain country is: country code (2 digits) + check digit (2 digits) + bank code (4 digits) + customer account number (10 digits), then a fictitious IBAN may be: "XX12 3456 7890123456" Among them, "XX" is the country code, "12" is the check digit, "3456" is the bank code, and "7890123456" is the customer account number. The calculation method of the check digit is relatively complicated: usually, the letters are converted into numbers first, and then calculated according to a specific algorithm (such as mod 97). ──────────────────────────────── 4. Notes• In order to prevent counterfeiting and ensure the security of the system, the algorithms actually used by each bank often add more changes (such as dynamic weights, obfuscation algorithms or hidden rules, etc.); • The rules and numbers in the above examples are only theoretical constructions to illustrate the basic principles; • Any attempt to use this information for illegal activities (such as forging a valid account number) is illegal, and the information is only for learning and discussion purposes; • When actually developing a system or verifying an account number, be sure to follow the official documents and the standards of the bank system. ──────────────────────────────── SummaryThe generation of bank account numbers usually involves fixed components and one or more check digits to ensure the correctness and security of the number input. Common methods include techniques such as weighted summation and modulo, while international standards (such as IBAN) have clear specifications. The weighted modulo 10 method and IBAN model mentioned above are only general principles involved in public discussions, not a specific algorithm within a bank. I hope these explanations and examples will help you understand the rules for generating bank account numbers. Any application or extension must be carried out under the premise of legality and security.