# Rules for generating personal identification numbers Personal identification numbers (such as resident ID numbers) usually follow a specific structure and algorithm. Take the mainland Chinese resident ID number as an example： ## 18-digit ID number structure 1. **Area code**: The first 6 digits indicate the administrative division code of the place of household registration 2. **Date of birth**: Middle 8 digits, the format is YYYYMMDD 3. **Sequence code**: Digits 15-17, the number of people born on the same day in the same area, of which the 17th odd number represents a male and the even number represents a female. 4. **Check code**: The last 1 digit, calculated from the first 17 digits ## Example of generation method Suppose the first 17 digits are: `440101199001011234` Check code calculation steps： 1. Multiply the first 17 digits by the corresponding weighting factor (7,9,10,5,8,4,2,1,6,3,7,9,10,5,8,4,2) 2. Add and sum the products 3. Divide the sum by 11 to take the remainder 4. Look up the table according to the remainder (0→1,1→0,2→X,3→9,4→8,5→7,6→6,7→5,8→4,9→3,10→2) Get the check code ## Sample example -110101199003074796 (Beijing, born on March 7, 1990, male) -440102199207215889 (Guangzhou City, Guangdong Province, born on July 21, 1992, female) -320583199412158721 (Kunshan City, Jiangsu Province, born on December 15, 1994, male) Please note that the above examples are all generated by simulation and do not correspond to real personal information. The actual ID number is strictly protected and should not be shared or used at will.