The following explanation mainly uses the structure of the US Social Security Number (SSN) as an example. Because the rules and uses of social security numbers may vary from country to country, please confirm which country's rules you need. The following introduces the basic structure and (historical) generation rules of the US SSN. At the same time, several fictitious numbers are provided for demonstration purposes only. Please note that these numbers are for demonstration purposes only and do not represent the actual allocation rules, nor should they be used for any illegal purposes. ──────────────────────────────── 【Basic format of SSN】 The US Social Security Number consists of nine digits, usually written in three parts, in the format of AAA–GG–SSSS, where: ① AAA - "Area Number": originally determined by a certain area where the applicant is located (before randomization in 2011, each state had a certain distribution pattern). ② GG - "Group Number": used to group numbers issued in the same area. The allocation order is not a simple numerical order, but follows the order specified by the government (for example, odd-numbered numbers are allocated first, followed by spouse-numbered numbers). ③ SSSS —— “Serial Number”: An increasing serial number within the same group, used to distinguish specific applicants. ──────────────────────────────── 【Example Explanation】 The following are two purely fictitious example numbers to help you understand the functions of each part: Example 1: 123–45–6789 • Area number “123”: Under historical rules, this represents a certain geographical area where the applicant was originally located. • Group number “45”: Indicates the number obtained according to the group allocation rule in area “123”. • Serial number “6789”: It is the 6789th number in this area and group (for illustration only, not the actual order). Example 2: 231–98–7654 • Area number “231”: Similarly, it represents a certain area in history. • Group number “98”: A number obtained according to the internal grouping rule. • Serial number “7654”: Indicates the sequential serial number under this grouping. ──────────────────────────────── 【Generation rules and changes】 1. Historically, the area code of SSN has always been related to the zip code or state when the applicant first registered, so there may be continuity of area codes in the same area. 2. The allocation of group numbers is not simply incremental, but follows the allocation order stipulated by the government (for example, first allocate in odd order, then in even order); this requires reference to the historical rules announced by the government when verifying the number. 3. The sequence number is the sequential number within each (area code + group number) combination. 4. After 2011, the US Social Security Administration began to use randomization procedure to allocate SSN. The area number, group number and sequence number no longer clearly reflect the applicant's geographic information or application order. This measure is mainly to improve the security of the number and prevent identity theft. ──────────────────────────────── 【Notes】 • The above example numbers are fictitious, and any coincidence with real numbers in the system is purely accidental. • The actual number generation process involves historical statistics and security considerations. The detailed rules belong to the internal management regulations of the US government and should not be used to infer or forge real numbers. • If you are looking up the social security number of another country (such as China), you need to note that different countries and regions have different numbering rules and management methods, which generally involve joint management by multiple departments, and the specific rules may not be public. ──────────────────────────────── 【Summary】 - The US SSN originally used a "three-segment" number composition: area number, group number, and serial number. - Historically, the area number reflects the geographic location, and the group number and serial number are used for internal numbering; a randomization strategy has been adopted since 2011. - Example 1 (123–45–6789) and Example 2 (231–98–7654) are only used to illustrate the composition and meaning of each part. Do not use them in any actual business. I hope the above explanation can help you understand the structure and basic generation rules of the social security number. If you have any other questions, please let me know.