The composition of the bank card number (i.e. Primary Account Number, PAN) follows international standards (ISO/IEEE 7812), and its structural design can not only identify the card issuer, but also ensure uniqueness and verification validity. The following is a detailed description of its composition and generation logic： --- ###**1. The basic structure of the bank card number** A typical 16-digit bank card number (such as VISA, MasterCard, and UnionPay) is usually divided into four parts： 1. **Card issuer identifier (IIN)**: The first 6 digits (4 or 8 digits for some institutions) identify the card issuer and card type. 2. **Account identifier**: 6-12 digits in the middle, customized by the card issuer. 3. **Check code**: The last 1 digit (generated by Luhn algorithm). 4. **example**：`6225 8866 8888 1234`（ Fictitious card number). --- ###**Two, detailed decomposition** #### **1. Card issuer identifier (IIN/BIN)** -**The first 6 digits** are called BIN (Bank Identification Number), for example： -*****: Start with `4` (such as `412345`). -**MasterCard**: Start with `51-55' or `2221-2720'. -**China Unionpay**: Start with `62' (for example, `622588' is a debit card of China Merchants Bank). -**American Express**: Start with `34' or`37'. -**Function**: Identify the issuing bank, card type (debit/credit card) and card level (general card, gold card, etc.). #### **2. Account identifier** -**The number of intermediate digits**is allocated by the card issuer and usually contains the following information： -Branch code (optional). -Account type (such as savings account, credit card account). -Randomly generated or sequentially assigned serial numbers (to ensure uniqueness). #### **3. Check code (last 1 digit)** -Generated using the **Luhn algorithm** (modulo 10 algorithm) to verify the validity of the card number input. --- ###**3. Example of Luhn algorithm** Take the fictitious card number `6225 8866 8888 123X` (X is the check code to be calculated) as an example： 1. **From right to left, even digits multiplied by 2** (check code X is temporarily ignored)： ``` Original number：6 2 2 5 8 8 6 6 8 8 8 8 1 2 3 X Even digits：6 2 8 8 8 8 1 3 → After multiplying by 2: 12 4 16 16 16 16 2 6 ``` 2. **Add the sum of the product**： ``` 1+2 +4 +1+6 +1+6 +1+6 +1+6 +2 +6 = 44 ``` 3. **Odd digits are directly added**： ``` 2 +5 +8 +6 +8 +8 +2 = 39 ``` 4. **Sum + odd digit sum = 44 + 39 = 83** 5. **Calculate the check code X**: make the sum +X mod0mod10→X=7 (83+7=90, divisible by 10). The final card number is: `6225 8866 8888 1237'. --- ###**Fourth, the card number generation process** 1. **Determine the card issuer**: Select IIN (such as UnionPay card starting with 62). 2. **Allocation of BIN**: The bank applies for a unique BIN (such as China Merchants Bank `622588`). 3. **Generate account number**： -Allocate intermediate digits (such as area code + random number) according to internal rules. -Ensure uniqueness (avoid duplication). 4. **Calculate the check code**: The last digit is generated by the Luhn algorithm. 5. **Bind account**: Associate the card number with the user account and write it to the banking system. --- ###**5. Examples of different card organizations** -**VISA**：`4***** ****** *** X` (such as the test number of `4111 1111 1111 1111`). -**MasterCard**：`51**** ****** *** X` (such as `5555 5555 5555 4444`). -**Unionpay Card**：`62**** ****** *** X` (such as `6225 8866 8888 1237`). --- ###**6. Safety tips** -**Card number uniqueness**: Ensure global uniqueness through BIN allocation and internal rules. -**Check code function**: Prevent input errors or forgery, but cannot resist malicious attacks. -**Privacy protection**: Do not disclose the complete card number, CVV and expiration date. Through the above structure, the bank card number is efficiently verified while ensuring uniqueness. It is a payment system.