CHEN, C.-P.; QI, F. Completely monotonic function associated with the Gamma functions and proof of Wallis’ inequality. **Tamkang Journal of Mathematics**, *[S. l.]*, v. 36, n. 4, p. 303–307, 2005. DOI: 10.5556/j.tkjm.36.2005.101. Disponível em: https://journals.math.tku.edu.tw/index.php/TKJM/article/view/101. Acesso em: 19 aug. 2022.