ISBN 6006043351 is nu­me­rically correct (check­sum OK).
The ISBN 6006043351 that you input was found to be numerically correct. This only means that it is 10 or 13 digits long and that the last digit (the checksum digit) has got the correct value according to the checksum formula. Thus the ISBN cannot have been produced from a valid ISBN by a single error (change in one digit or transposition of two digits). This check does not prove that the ISBN has ever actually been assigned to a book. As a way to check it the ISBN corresponds to a book this site offers links to the following bookseller's sites: amazon.com (USA), amazon.co.uk (UK) und amazon.de (Germany). The start of the ISBN corresponds to none of the groups published by the International ISBN Agency as per 2003-05-19.	To the home page
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If these book sites do not know the ISBN this does not mean that there is no book with that ISBN - the book could have been issued decades ago, be from another country than those catered for by the Amazon sites, or it could be of minor commercial interest to those large bookshop sites. Additional sites to search by ISBN (in this case, in catalogs of libraries) are e.g. the Library of Congress (USA) or the search gateway of the Deutsche Bibliothek.

You can check another ISBN with this form.