The following content is only used to explain the structure and composition principle of various social security numbers (or similar identification numbers). Do not use them for any illegal purpose or forgery. In fact, the generation rules of social security numbers (or personal identification numbers) in different countries and regions are different, and the rules may also change with policy adjustments. The following are just two common examples: the structure of the US Social Security Number (SSN) and the generation rules of China's "Resident Identity Number" (used as one of the social security-related identifiers in many businesses) as examples to help understand their respective composition and verification mechanisms. ────────────────────────── 【I. US Social Security Number (SSN)】 1. Structure Description: • Traditionally, the US SSN is 9 digits, usually written in the format of "AAA-GG-SSSS", where: ○ AAA: Area Number. In the early days, it was related to the applicant's location and postal area (for example, the number range in some areas in the east was smaller); since 2011, it has been changed to random allocation. ○ GG: Group Number. It is used to indicate the order of number grouping for easy management, not a simple sequential arrangement. ○ SSSS: Serial Number. Generally, it is a serial number when the area and group numbers are combined. 2. Points to note: • Initially, the area number was assigned according to the state and region where the applicant was located (for example, New York, California, etc. have their own number ranges), and after a certain period of time, the US Social Security Administration implemented a randomization policy, breaking the original geographical association. • Verification algorithm: The traditional SSN does not have an obvious check digit like some national ID numbers, but the US government has a strict issuance process to avoid duplication and forgery. 3. Examples: Example 1: 123-45-6789 – “123” as an area number may represent a certain region (just as an example, the actual allocation rules are more complicated), – “45” as a group number, – “6789” as a serial number. Example 2: 237-03-4821 – Similarly, the three parts are combined to form a complete 9-digit SSN. ────────────────────────── 【II. Chinese Resident Identity Number (often used as a personal identifier for social security purposes)】 Chinese Resident Identity Number is often regarded as a very important personal identifier and is used in many businesses (such as social security, medical insurance, etc.). The generation rules of the 18-digit identity number are as follows: 1. Structure description: • The first 6 digits: area code – indicates the administrative division code of the applicant's registered residence. For example, "110105" may represent a district in Beijing. • The 7th to 14th digits: date of birth (YYYYMMDD format) – For example, "19491231" means born on December 31, 1949. • The 15th to 17th digits: sequence code – used to distinguish different people born on the same day in the same region, where odd numbers generally identify males and even numbers identify females. • The 18th digit: check code – derived from the modulo-11 weighted algorithm based on the first 17 digits. The specific algorithm process is as follows: ① Multiply the first 17 digits by the corresponding weights in order (the weight order is generally: 7, 9, 10, 5, 8, 4, 2, 1, 6, 3, 7, 9, 10, 5, 8, 4, 2). ② Sum the products obtained. ③ Divide this sum by 11, and the remainder corresponds to a specific check code (the correspondence between the remainder and the check code is generally: 0→1, 1→0, 2→X, 3→9, 4→8, 5→7, 6→6, 7→5, 8→4, 9→3, 10→2). 2. Example: Example: 11010519491231002X – “110105”: represents the district code of a certain Beijing city. – “19491231”: date of birth, that is, December 31, 1949. – “002”: Sequence code, where “2” is an even number, usually indicating a female. – “X”: The final check digit. Assuming that the remainder calculated by the above weighted algorithm is 2, the check digit is mapped to “X”. 3. Other notes: • Some early versions of ID cards use a 15-digit format, which is similar to the 18-digit format, but the date of birth is only recorded as “YYMMDD” and there is no independent check digit; the current system has been upgraded to 18 digits. ────────────────────────── 【Summary】 1. Educational purpose: – The generation rules of the above two numbers are public information, mainly used to explain their digital structure and check design. For the US SSN, although there were historically concepts of area and group numbers, random allocation is currently used to avoid geographical associations; while China’s 18-digit ID card number has a rigorous structure, and weighted summation and modulo 11 operations are used to ensure number accuracy and anti-counterfeiting capabilities. 2. Security and legality: – Emphasize that the introduction here is only for understanding the number structure and check principle, and shall not be used for forgery, impersonation or any other illegal purposes. The actual number generation and authentication is carried out by government agencies in each country (or region) in accordance with strict procedures and confidentiality measures. 3. Other countries and regions: – In addition to the above examples, the rules of social security or personal numbers in other countries are also unique. Some may contain letters, separators or other verification algorithms. Those interested can refer to the official instructions or technical documents of each country. I hope the above introduction can help you better understand the composition logic and design principles of different social security numbers (or identity numbers). If you have further questions, please indicate the specific country or region so that more accurate information can be provided.