Error: min/max value in number fields
Numbers have certain limits in computer systems and storing (as well as working with) exceptionally large ones is cumbersome.

In the database, the int (integer, a whole number) is limited to a range from -2147483648 to 2147483647. A bigint can range from -9223372036854775808 to 9223372036854775807 but is less common. And I don't think Craft uses bigints anywhere.

I know it's purely numerical, but could your ISBN numbers use a text field? Unless you're doing math on it then this should suffice. If you really want you could a new fieldtype that validates an ISBN number but saves as a varchar in the DB.