The following are two examples of publicly known national ID number generation and verification algorithms used to prevent input errors. The examples here are only for academic research and understanding of their principles, and do not represent recommendations for direct application in actual systems. Note that the ID number designs of different countries have their own characteristics, and their generation rules often involve information such as area codes, date of birth, serial numbers, etc., and are supplemented by verification algorithms to ensure the correctness of the numbers. The following two examples are typical: ──────────────────── 【Example 1: Chinese Resident Identity Card Number (18 digits) 】 The Chinese Identity Card Number consists of 18 digits (the last digit may be a capital letter "X"), and its composition is roughly as follows: 1. The first 6 digits: area code (indicating the jurisdiction of the issuing authority) 2. The next 8 digits: date of birth (format: YYYYMMDD) 3. Another 3 digits: sequence code (usually used to distinguish different people born on the same day, odd numbers generally represent males and even numbers represent females) 4. The last digit: check digit The check digit is calculated using the weighted sum modulo method. The basic steps are as follows: 1. Assign fixed weight factors to the first 17 digits in the order: W = {7, 9, 10, 5, 8, 4, 2, 1, 6, 3, 7, 9, 10, 5, 8, 4, 2} 2. Record the first 17 digits as A1, A2, …, A17, calculate the weighted sum: S = A1×7 + A2×9 + A3×10 + A4×5 + A5×8 + A6×4 + A7×2 + A8×1 + A9×6 + A10×3 + A11×7 + A12×9 + A13×10 + A14×5 + A15×8 + A16×4 + A17×2 3. Calculate the remainder: R = S mod 11 4. According to the remainder R, the corresponding relationship of the check code is obtained. The general mapping relationship is as follows (the order given in some literature may be slightly different, but the most common is): R: check code 0: 1 1: 0 2: X 3: 9 4: 8 5: 7 6: 6 7: 5 8: 4 9: 3 10: 2 5. Attach the corresponding check code to the 18th bit. For example, the pseudo code is expressed as: ------------------------------------------------ function calculateChineseIDChecksum(first17Digits): weights = [7, 9, 10, 5, 8, 4, 2, 1, 6, 3, 7, 9, 10, 5, 8, 4, 2] mapping = {0:'1', 1:'0', 2:'X', 3:'9', 4:'8', 5:'7', 6:'6', 7:'5', 8:'4', 9:'3', 10:'2'} sum = 0 for i from 0 to 16: sum += int(first17Digits[i]) * weights[i] r = sum mod 11 return mapping[r] ------------------------------------------------ ──────────────────── 【Example 2: Spanish National Identity Card (DNI/NIF)】 The Spanish identity card number (DNI) is usually in the form of 8 Arabic numerals followed by a check letter. The check letter is calculated as follows: 1. Take the 8-digit number as an integer and take the modulus of 23: R = number mod 23 2. Select the corresponding letter from the predefined letter sequence according to the remainder R. The commonly used letter sequence is: "TRWAGMYFPDXBNJZSQVHLCKE", that is, index 0 corresponds to 'T', index 1 corresponds to 'R', and so on to index 22 corresponds to 'E'. The pseudocode example is as follows: ------------------------------------------------ function calculateSpanishDNI(number): letters = "TRWAGMYFPDXBNJZSQVHLCKE" index = number mod 23 return letters[index] ------------------------------------------------ For example, if the number part is 12345678, the letter corresponding to the remainder obtained by calculating 12345678 mod 23 is the check code letter, and the final DNI is "12345678X" (assuming that the letter corresponding to the remainder is X). ────────────────────── 【Other Notes】 1. Social Security Number (SSN) in the United States The SSN in the United States usually consists of nine digits and does not have a check code mechanism like the above. Its allocation follows certain historical rules and coding principles (for example, the area code is related to the place of birth or application time), but the specific generation method is not a single mathematical algorithm, and the current allocation method has been greatly adjusted to avoid problems such as regional inference. 2. Japan's "マイナンバー" (personal number) Japan's personal number system also uses a check digit, and its design refers to the idea of the Luhn algorithm, but the specific algorithm details are explained in public documents. Many countries use similar check code mechanisms to prevent incorrect number input. It should be noted that in addition to identifying individuals, the ID card numbers of various countries also incorporate various considerations such as local management and statistics. Therefore, although the check algorithm itself may look simple, the other components of the number (such as area code, date of birth code, etc.) are often based on strict administrative planning. In addition, if used for actual system design, data verification or security anti-counterfeiting, it is also necessary to pay attention to the anti-counterfeiting design and data protection of the number. I hope that the above introduction to the generation and verification algorithms of Chinese and Spanish ID card numbers can help you understand some typical ideas in the design of different countries.