Asymptotic approximation of central binomial coefficients with rigorous error bounds

We show that a well-known asymptotic series for the logarithm of the central binomial coefficient is strictly enveloping in the sense of Pólya and Szegö, so the error incurred in truncating the series is of the same sign as the next term, and is bounded in magnitude by that term. We consider closely related asymptotic series for Binet's function, for \(\ln\Gamma(z+\frac12)\), and for the Riemann-Siegel theta function, and make some historical remarks.

INTEGRAL REPRESENTATIONS AND INEQUALITIES OF EXTENDED CENTRAL BINOMIAL COEFFICIENTS

In the paper, the author presents three integral representations of extended central binomial coefficient, proves decreasing and increasing properties of two power-exponential functions involving extended (central) binomial coefficients, derives several double inequalities for bounding extended (central) binomial coefficient, and compares with known results.

Central binomial coefficients divisible by or coprime to their indices

Let [Formula: see text] be the set of all positive integers [Formula: see text] such that [Formula: see text] divides the central binomial coefficient [Formula: see text]. Pomerance proved that the upper density of [Formula: see text] is at most [Formula: see text]. We improve this bound to [Formula: see text]. Moreover, let [Formula: see text] be the set of all positive integers [Formula: see text] such that [Formula: see text] and [Formula: see text] are relatively prime. We show that [Formula: see text] for all [Formula: see text].