Bank Card Number (Bank Card Number) is a unique identifier used to identify a bank card, usually composed of a set of numbers. Different bank card organizations (such as Visa, MasterCard, UnionPay, etc.) have their own numbering rules, but generally follow the international standard ISO/IEC 7812. The following is a general description of the composition of the bank card number, and takes a virtual bank card number as an example for analysis. --- ### Composition of bank card number The bank card number is usually composed of **13 to 19 digits**, the specific composition is as follows： 1. **Issuing bank Identification Number (Issuer Identification Number, IIN)** -The first 6 digits are used to identify the issuing bank or financial institution. - For example: Visa card starts with 4, MasterCard starts with 5, and UnionPay card starts with 62. 2. **Personal Account Identification number (Individual Account Identification)** -The 7th to the penultimate digit is used to identify the cardholder's account information. -This part of the number is allocated by the issuing bank and is usually related to account type, branch office and other information. 3. **Check digit (Check Digit)** -The last 1 digit is used to verify the validity of the bank card number. -The check digit is calculated by the ** Luhn algorithm** to prevent input errors or forgery. --- ### Example analysis Suppose there is a bank card number:**6225 8801 2345 6789** We break it down as follows： 1. **Issuing bank identification number (IIN)** -First 6 digits:**622588** -Among them,**62** Represents a Unionpay card,**2588** Is the specific code of the issuing bank. 2. **Personal account identification number** -7th to penultimate 2nd place: **012345678** -This part is allocated by the issuing bank and is used to identify account information. 3. **Parity bit** -Last 1 digit: **9** -Verify the validity of the entire number through the Luhn algorithm. --- ### Introduction to Luhn algorithm The Luhn algorithm is a simple verification method used to verify the validity of numbers such as bank card numbers. The steps are as follows： 1. From right to left, multiply the even digits by 2. 2. If the result of multiplying by 2 is greater than 9, the numbers of the result are added (or subtracted by 9). 3. Add all numbers, including odd digits that are not multiplied by 2. 4. If the sum is a multiple of 10, the number is valid. --- ### Precautions -The bank card number is sensitive information, so do not disclose it at will. -The length and rules of bank card numbers in different countries and regions may be slightly different. -The issuing bank is responsible for the generation and distribution of the actual bank card number, and strict encryption and security management measures are followed. Hope the above information is helpful to you! If you have any other questions, feel free to ask questions.