[1] B. C. Berndt, Number Theory in the Spirit of Ramanujan, Student
Mathematical Library, Vol. 34, American Mathematical Society,
Providence, RI, 2006.
[2] S. Cooper and M. D. Hirschhorn, On the number of primitive
representations of integers as sum of squares, Ramanujan Journal 13
(2007), 7-25.
[3] S. Cooper and H. Y. Lam, On the Diophantine equation Journal of Number Theory 133 (2013),
719-737.
[4] L. E. Dickson, Introduction to the Theory of Numbers, University
of Chicago Press, Reprint (1957), Dover Publications, 1929.
[5] W. Hürlimann, Exact and asymptotic evaluation of the number of
distinct primitive cuboids, Journal of Integer Sequences 18(2),
Article 15.2.5. (2015).
[6] E. Grosswald, Representations of Integers as Sums of Squares,
Springer, New York, 1985.
[7] J. L. Lagrange, Démonstration d‘un théorème
d’arithmétique, Nouveaux Mémoires de l’Acad.
Royale des Sciences et Belles Lettres de Berlin, (Oeuvres 3 (1770),
695-795).