The structure of the credit card number follows international standards (ISO/IEC 7812) and mainly consists of the following parts： 1. **Issuing bank identification number (IIN/BIN)**: The first 6 digits identify the issuing institution (for example, Visa starts with 4 and Mastercard starts with 5). 2. **Personal account ID**: The 7th to the penultimate digit is assigned by the issuing bank. 3. **Check digit**: The last digit, verify the validity of the number through the **Luhn algorithm**. --- ###**Example number (only used to illustrate the structure, not the real card number)** -*****:`4xxx-xxxx-xxxx-xxxx` (such as `4111-1111-1111-1111'test number) -**Mastercard**: `5xxx-xxxx-xxxx-xxxx` (such as '5555-5555-5555-4444'test number) -**American Express**: `34xx-xxxxxx-xxxxx' (such as '3782-822463-10005'test number) --- ###**Generation method** 1. **Luhn algorithm verification**： -From right to left, even digits×2 (if the result is ≥9, minus 9). -The sum of all numbers must be divisible by 10. *Example*: Check digit calculation (assuming the first 15 digits are `7992739871x`)： ``` 7×2 + 9 + 9×2 + 2 + 7×2 + 3 + 9×2 + 8 + 7×2 + 1 = 64 Parity bit = (10 - 64%10) = 6 → Complete card number: 79927398716 ``` 2. **Issuing bank rules**: The issuing institution assigns the range of IIN and account number to ensure uniqueness. --- ###**Important reminder** -**It is strictly prohibited to generate or use real card numbers**, which may involve legal risks. -When testing, please use the ** sandbox test number** provided by the payment platform (such as the public test numbers of Stripe and PayPal). For further technical details, it is recommended to refer to the PCI DSS standard or the documentation of the banking institution.