The rules for generating bank card numbers usually follow international standards, such as ISO/IEC 7812, especially the ISO/IEC 7812-1 standard. This standard defines the format and verification algorithm of the bank card number. The following are some key points and the generation and interpretation of sample numbers： ### 1. **Composition of bank card number** -**Issuing bank identification number (IIN)**: The first 6 digits are used to identify the issuing bank or financial institution. -**Personal account identification**: The next few digits are used to identify the specific account. -**Check digit**: The last digit is used to verify the validity of the card number. ### 2. **Luhn algorithm** -**Luhn algorithm**: Used to verify the validity of the bank card number. It is a simple verification algorithm that can detect common input errors. ### 3. **Sample number** -**Visa card**: Usually starts with 4 and has a length of 16 digits. For example: `4111 1111 1111 1111`. -**MasterCard**: Usually starts with 51-55 or 2221-2720, and the length is 16 digits. For example: `5500 0000 0000 0004`. -**American Express**: Usually starts with 34 or 37 and has a length of 15 digits. For example: `3782 8224 6310 005`. -**Discover Card**: Usually starts with 6011, 65 or 644-649, and the length is 16 digits. For example: `6011 0000 0000 0004`. ### 4. **Steps to generate a bank card number** -**Select the issuing bank identification number (IIN)**: Select the appropriate IIN according to the card type. -**Generate personal account ID**: Randomly generated or generated according to specific rules. -**Calculate the check digit**: Use the Luhn algorithm to calculate the check digit. ### 5. **Calculation steps of Luhn algorithm** 1. Starting from the penultimate digit of the card number, multiply by 2 every other digit. 2. If the product is greater than 9, the numbers of the product are added. 3. Add all numbers, including numbers that are not multiplied by 2. 4. The parity bit is a number such that the sum is a multiple of 10. ### 6. **example** Suppose we want to generate a Visa card number, the IIN is `4111 11`, and the personal account ID is `1111 1111`. 1. Generate an unverified card number: `4111 1111 1111 111` 2. Calculate the parity bit using the Luhn algorithm： - 4*2 + 1 + 1*2 + 1 + 1*2 + 1 + 1*2 + 1 + 1*2 + 1 + 1*2 + 1 + 1*2 + 1 = 8 + 1 + 2 + 1 + 2 + 1 + 2 + 1 + 2 + 1 + 2 + 1 + 2 + 1 = 24 -24 + parity bit = 30 (the nearest multiple of 10) -Parity bit = 6 3. Complete card number: `4111 1111 1111 1116` ### 7. **Precautions** -The generated card number is only used for testing and examples, and cannot be used for actual transactions. -The issuing bank is responsible for the generation and distribution of the actual bank card number, and strict rules and standards are followed. Through the above steps, you can understand the rules for generating bank card numbers and generate some sample numbers for testing or learning.