1. Andreescu, T., Andrica, D., Cucurezeanu, I.: An Introduction to Diophantine Equations. Birkhäuser, New York (2010)
2. Cassels, J.W.S.: Rational Quadratic Forms. Dover Publications, Mineola (2008)
3. Dickson, L.E.: Modern Elementary Theory of Numbers. University of Chicago Press, Chicago (1939)
4. Dickson, L.E.: History of the Theory of Numbers, vol. II. Dover Publications, Mineola (2005)
5. Guy, R.: Unsolved Problems in Number Theory, 3rd edn. Springer, New York (2004)