Asymptotic Formulas and Inequalities for the Gamma Function in Terms of the Tri-Gamma Function

Approximation for the gamma function via the tri-gamma function

In this paper, we present a new sharp approximation for the gamma function via the tri-gamma function. This approximation is fast in comparison with the recently discovered asymptotic series. We also establish the inequalities related to this approximation. Finally, some numerical computations are provided for demonstrating the superiority of our approximation.

Asymptotic Formulas for the Gamma Function by Gosper

The main aim of this paper is to give two general asymptotic expansions for the gamma function, which include the Gosper formula as their special cases. Furthermore, we present an inequality for the gamma function. Mathematics subject classification (2010): Primary 33B15; Secondary 41A60.

Inequalities for the Gamma Function

We prove the following two theorems: (i) Let Mr(a, b) be the rth power mean of a and b. The inequality Mr(Γ(x), Γ(1/x)) ≥ 1 holds for all x ∈ (0,∞) if and only if r ≥ 1/C − π2/(6C2), where C denotes Euler’s constant. This refines results established by W. Gautschi (1974) and the author (1997). (ii) The inequalities xα(x−1)−C < Γ(x) < xβ(x−1)−C (∗) are valid for all x ∈ (0, 1) if and only if α ≤...

Monotonicity and inequalities for the gamma function

Inequalities for Gamma Function Ratios

Write R(x, y) = Γ(x + y) Γ(x). Inequalities for this ratio have interesting applications, and have been considered by a number of writers over a long period. In a Monthly article [7], Wendel showed that x(x + y) y−1 ≤ R(x, y) ≤ x y for 0 ≤ y ≤ 1. (1) Wendel's method was an ingenious application of Hölder's inequality to the integral definition of the gamma function. Note that both inequalities ...