1. Abramowitz, M., Stegun, I.A.: Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables. Dover Publications, New York (1965)
2. Agarwal, R.P., Xu, B., Zhang, W.: Stability of functional equations in single variable. J. Math. Anal. Appl. 288, 852–869 (2003)
3. Brydak, J.: On the stability of the functional equation $$\varphi [f(x)]=g(x)\varphi (x)+F(x)$$ φ [ f ( x ) ] = g ( x ) φ ( x ) + F ( x ) . Proc. Am. Math. Soc. 26, 455–460 (1970)
4. Brzdek, J., Brillouët-Bellout, N., Ciepliński, K.: On some recent developments in Ulam’s type stability. Abstr. Appl. Anal. (2012) Art ID. 716936
5. Brzdek, J., Popa, D., Xu, B.: The Hyers-Ulam stability of linear equations of higher orders. Acta Math. Hung. 120, 1–8 (2008)