ISBN prefix

How to sell modular arithmetic to students only interested in literature? Well, try to explain the structure of ISBN-numbers “The ISBN (International Standard Book Number) is a unique machine-readable identification number, which marks any book unmistakably. This number is defined in ISO Standard 2108. The number has been in use now for 30 years and has revolutionised the international book-trade. 166 countries and territories are officially ISBN members. The ISBN accompanies a publication from its production onwards.” The ISBN-number of a book is a ten-digit number divided into four parts, separated by hyphens telling you a lot about the ambitions and location of the book’ publisher. I’ll explain some of it by telling how I obtained the barcode for the first book to be published by neverendingbooks.org (see picture). The first part is the group identifier and identifies a country, area or language area participating in the ISBN system. For the Netherlands and the Flemish speaking part of Belgium this identifier is 90. Hence, depending on your location you have to approach different agencies in order to obtain an ISBN-number. If you are living in the US all you have to do is to invent a name for your PublishingHouse, get your Visa-card out and visit isbn.org . For smaller groups the process is more personal. The first time I tried to apply for an ISBN-number with De Boekenbank I messed up and got immediately an email telling me what I did wrong. I replied explaining what NeverEndingBooks had in mind and asked advice on how to set it up properly. I’m sure I’ll need this personal contact again in the near future. The second part is the Publisher Identifier or prefix. I didn’t know this before but the very definition of a publisher is the person or company registering a book’s ISBN. Hence, if you intend to publish a series of books your local ISBN-agency has to reserve a certain amount of ISBN-numbers for you, all having the same start-block (the prefix). The shorter the prefix the more ambitious the PublishingHouse. The registered prefix of NeverEndingBooks is 90809390 which tells the experienced ISBN-watcher that we intend in the next years to publish “only” ten books. If you have more energy you can also apply for a series of 100, 1000 or even 10000 ISBN-numbers but the amount of money needed to register these series increases quickly‚Ķ The third part of the ISBN-number is the title identifier so for our first book it is just 1. However, in order to register it you have to provide the agency (minimally) with a title and publication date (fortunately, author, price, number of pages etc. are optional at this stage). Anyway, the first real deadline for NeverEndingBooks will be may 15th 2005! And now it is time to return to modular arithmetic, the fourth part is a check digit. The check digit is the last digit of an ISBN. It is calculated on a modulus 11 with weights 10-2, using X in lieu of 10 where ten would occur as a check digit. This means that each of the first nine digits of the ISBN excluding the check digit itself is multiplied by a number ranging from 10 to 2 and that the resulting sum of the products, plus the check digit, must be divisible by 11 without a remainder. In our case, we have the following numbers(weights) 9(10) 0(9) 8(8) 0(7) 9(6) 3(5) 9(4) 0(3) 1(2) We have to multiply the numbers with their weight and add them all up, 90+0+64+0+54+15+36+0+2=261=8(mod 11) whence the check digit should be 3. For example, I know already that the ISBN-number of the second book to be published by NeverEndingBooks will be 90-809390-2-1 but, due to lacking information, it will take a while before it can be registered.