APA (7th ed.) Citation

Guy, R. K. (1981). Unsolved problems in number theory. Springer-Verlag.

Chicago Style (17th ed.) Citation

Guy, Richard K. Unsolved Problems in Number Theory. New York: Springer-Verlag, 1981.

MLA (8th ed.) Citation

Guy, Richard K. Unsolved Problems in Number Theory. Springer-Verlag, 1981.