If you have ever bought a book, you might have noticed a barcode and a number on its back cover. This number is called the International Standard Book Number (ISBN) and it is used to uniquely identify a book and its publisher. ISBNs are also useful for libraries, booksellers, distributors and readers who want to find or order a specific book. But did you know that ISBNs are not just random numbers? They are actually based on a mathematical formula that allows them to detect errors and prevent confusion. In this blog post, we will explore how ISBNs work and what kind of mathematics they use. What is an ISBN? An ISBN is a numeric commercial book identifier that is intended to be unique. Publishers purchase or receive ISBNs from an affiliate of the International ISBN Agency. An ISBN is assigned to each separate edition and variation (except reprintings) of a publication. For example, an e-book, a paperback and a hardcover edition of the same book will each have a different ISBN. The ISB