1. Abramowitz, M., Stegun, I. (eds.): Handbook of Mathematical Functions with Formulas, Graphs and Mathematical Tables. Dover, New York (1972)
2. Alzer, H.: A refinement of the Cauchy-Schwarz inequality. J. Math. Anal. Appl. 168, 596–604 (1992)
3. Buzano, M.L.: Generalizzazione della diseguaglianza di Cauchy-Schwarz (Italian). Rend. Sem. Mat. Univ. e Politech. Torino. 31(1971/73), 405–409 (1974)
4. Cerone, P., Dragomir, S.S.: Some applications of de Bruijn’s inequality for power series. Integral Transform. Spec. Funct. 18(6), 387–396 (2007)
5. de Bruijn, N.G.: Problem 12. Wisk. Opgaven 21, 12–14 (1960)