References
- M. Albert and J. A. Baker, Bounded solutions of a functional inequality, Canad. Math. Bull. 25 (1982), no. 4, 491-495. https://doi.org/10.4153/CMB-1982-071-9
- R. Blecksmith and S. Broudno, Equal sums of three fourth powers or what Ramanujan could have said, Math. Magazine 79 (2006), 297-301. https://doi.org/10.2307/27642955
- E. A. Chavez and P. K. Sahoo, On a functional equation arising from number theory, Appl. Math. Lett. 24 (2011), no. 3, 344-347. https://doi.org/10.1016/j.aml.2010.10.020
- D. H. Hyers, G. Isac, and Th. M. Rassias, Stability of Functional Equations in Several Variables, Birkhauser, 1998.
- P. K. Sahoo and Pl. Kannappan, Introduction to Functional Equations, CRC Press, Taylor & Francis Group, Boca Raton, 2011.