I didn't see this question here yet so I thought I would ask if someone has the formula for converting a 10 digit ISBN to a 13 digit ISBN and vice-versa. I know there are several sites that offer conversion such as ISBN.org from Bowker and a few spreadsheets that have macros for it but someone might find the formula useful.
Wikipedia gives it as
- Remove the ISBN 10 check digit from the end
- Add 978 to the front
- Add the ISBN-13 check digit to the end
The check digit is calculated as per Wikipedia
- Take each digit as an element in in an array x_ i.e. the ith digit i the ISBN is x_i e.g. x4 is the 4th digit.
- Multiply the even digits by 3 and sum these.
- add these to the sum of the odd digits
- find the remainder mod 10
- subtract from 10 (you have a number 1-10)
This is the result as a number between 1 and 10, unless the figure is 10 then the result is 0
x_13 = (10 - (x_1 + 3x_2 + x_3 + 3x_4 + ... + x_11 + 3x_12) mod10 ) mod 10