The ISBN of The Four Fundamental Concepts of Psychoanalysis is 0-393-00079-6.
The ISBN of The Four Loves is 0156329301.
The ISBN of Crisis Four is 9780552152365.
The ISBN of I Am Number Four is 0-061-96955-9.
The ISBN of Fantastic Four is 0-7851-1828-4.
The ISBN of Nineteen Eighty-Four is 978-0452284234.
The ISBN of Four Ways to Forgiveness is 0-06-105234-5.
The ISBN of Four Moons of Darkover is 0-88677-305-9.
The ISBN of Four Past Midnight is 978-0-670-83538-6.
The ISBN of The Twenty-Four-Inch Home Run is 9780809243419.
The ISBN of The First Four Years - novel - is 0-590-48813-9.
The ISBN of The Summoned is 0-7434-0700-8.
The ISBN of Concrete Mathematics is 0201558025.