References
- Conway , JH and Guy , RK . 1997 . The Book of Numbers , New York : Springer .
- Dickson , LE . 1920 . History of Numbers , Vol. II , New York : Chelsea . Dover reprint, 2005
- Hilbert , D and Cohn-Vossen , S . Geometry and the Imagination, 1932, AMS reprint, 1999