The International Standard Book Number (ISBN) is an international standard number used to identify books. Since June 2007, the ISBN has been extended from 1 0 to 13. It consists of five parts, namely ENA (European Commodity Number) book product code, group number, publisher number, book serial number and inspection number. In the above example, 978 is ENA code, which is a fixed book product code; 7 is the group number assigned by ISBN management agency to represent China; 5448 is the number of the publishing house, representing the code of a publishing house in China, which is allocated by the ISBN management organization in China, and its number depends on the number of documents published by the publishing house; 0275 is the book serial number, which is the number given to a book by this specific publishing house, and the publishing house is responsible for managing the distribution; 8 is a check code. The value of the check code is multiplied by 10 to 2 (called weighting) from the first nine digits. The sum of the products is divided by the modulus "1 1", and the remainder is subtracted from "1 1". When the check number is "10", it is indicated by "X". If the sum of "754480275" multiplied by 10 is divisible by 1 1, its check number is "0".