11 13 15 17 19 20 18 16 14 12

[hiflier]

On the publisher's page of many but by no means all books there is a series of numbers like those above. Usually increasing in a definite order and then decreasing similarly. What is the significance of this?

[Jomlett]

Well one is The International Standard Book Number (ISBN) is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code.

[Jomlett]

And there's also the printer’s key, also known as the number line, is a line of text printed on the copyright page (the verso of the title page) of books, used to indicate the print run. This how to recognize first and subsequent editions.