CRISTEA, V. G. (2015). A direct approach for proving Wallis ratio estimates and an improvement of Zhang-Xu-Situ inequality. Studia Universitatis Babeș-Bolyai Mathematica, 60(2), 201–209. Retrieved from https://studia.reviste.ubbcluj.ro/index.php/subbmathematica/article/view/5718