ISBN ISBN is a check digit method. It works by choosing the check digit c so that 11 divides
, where
are the 9 digits of the unenhanced number from left to right.
The ISBN method takes numbers of length 9 as input. It uses a base-11 method with an X standing for 10 in base 11. See The Mathematical Explorer: The ISBN Method
. See also: AddCheckDigit, VerifyCheckDigit, Mod11.
