The structure and generation rules of social security numbers (SSNs) vary from country to country. The following uses China's SSN as an example: ### China's SSN structure China's SSN is usually the same as the citizen ID number and follows the following structure: 1. **The first six digits (address code):** The administrative division code of the place of household registration. For example, `110000` represents Beijing. 2. **The middle eight digits (date of birth code):** The date of birth of the cardholder in the format of YYYYMMDD. For example, `19900101` represents birth on January 1, 1990. 3. **The last four digits (sequence code and check code):** - **The 17th digit (the third digit in the sequence code):** Gender identifier, an odd number indicates male, and an even number indicates female. - **The 18th digit (check code):** Calculated based on the first 17 digits using a specific algorithm to verify the legitimacy of the number. The check code may be a number from 0 to 9 or the letter X. ### Example Description The following is a fictitious social security number example to illustrate the structure: **Example number: 11010519900101123X** - **110105**: Administrative division code for Chaoyang District, Beijing. - **19900101**: Date of birth is January 1, 1990. - **123**: - **The 17th digit "3"**: Indicates that the person to whom the number belongs is male (odd number). - **X**: Check code, calculated from the first 17 digits to ensure the legitimacy of the number. ### Brief description of generation rules 1. **Address code** is determined based on the latest administrative division code released by the National Bureau of Statistics. 2. **Date of birth code** must conform to the actual date of birth, and the format is strictly YYYYMMDD. 3. **Sequence code** is usually numbered in sequence based on the number of births on the same day in the same region, with the 17th digit used to distinguish between genders. 4. **Verification code** is calculated by weighted factors and modulo 11 algorithm according to GB 11643-1999 standard to ensure the uniqueness and correctness of the entire number. ### Notes - **Confidentiality:** Social security number is sensitive personal information. Do not disclose it at will to prevent identity theft. - **Legal use:** Provide personal social security number only when it is legal and necessary, such as when handling related matters. The above information is for reference only. The specific structure and generation rules of social security number may change due to policy adjustments. For accurate information, please consult your local social security agency or relevant government department.