Hello, I just purchased a book and was thinking about the ISBN number wondering how many books could the current system contain.
How many books each with a unique ISBN number could there be with the current 13 digit numbers.
if all 0's count as one of the numbers there will be 1013 possibles : 10 000 000 000 000 (ten trillion)
I suspect that the is more coding written into the isbn number.
I was just looking at a book and the isbn number is split into 5 sections
3-1-3-5-1 (digits each)
One of those probably represents the publisher, one would be where it is published etc.
So not all number combinations could ever be used because you would run out of numbers in one section before another section would reach its limit.
It is good to be curious about the things we see and obviously, math-minded people are going to be curious about numbers.