ISBN

ISBN: International Standard Book Number

10-digit ISBN

The first 9 bits correspond to the country group, publisher and title. The last bit is used as a check-bit with a character from /[0-9X]/

(sum i * xi from 1 to 10) = 0

separate x_10 10 mod 11 === -1 mod 11

x_10 = (sum i * xi from 1 to 9) % 11