The book number of old books is usually composed of numbers and letters. Here are some common book number format of old books: - 080001: This is an international standard book number, which represents an international standard novel. - 0713: This is a Chinese novel. - 978-7-13: This is the title number used to identify the publication information of an e-book or journal. - 0471: This is the International Standard Book Number of the National Library of China, representing an international standard novel from the National Library of China. - 1234567890: This is the publication information of an e-book or digital publication. It should be noted that the book number format of old books may vary according to different countries or regions and different publishing institutions. In addition, some old books may be outdated or no longer in use, so there may be different book number format.