Definition:International Standard Book Number/ISBN-13

Definition
An international standard book number is an index number used to uniquely identify a published book.

The ISBN-$13$ format consists of a string of $12$ digits followed by a check digit.

The check digit $d$ is calculated as:


 * $d = \displaystyle \sum_{k \mathop = 1}^{12} k d_k \pmod {10}$