There is no X after the ID number in the household registration book, but there is an X after the ID number.
The ID number on your household registration book may be the first generation 15 digit, the last digit of the first generation 15 digit has no X, your ID number is the second generation 18 digit, and the last digit of the second generation 18 digit is the check code. The check code can be a number from 0 to 9, sometimes represented by X. ..