English

On asymptotics, Stirling numbers, Gamma function and polylogs

Combinatorics 2007-05-23 v1 Number Theory

Abstract

We apply the Euler--Maclaurin formula to find the asymptotic expansion of the sums k=1n(logk)p/kq\sum_{k=1}^n (\log k)^p / k^q, ~kq(logk)p\sum k^q (\log k)^p, ~(logk)p/(nk)q\sum (\log k)^p /(n-k)^q, ~1/kq(logk)p\sum 1/k^q (\log k)^p in closed form to arbitrary order (p,qNp,q \in\N). The expressions often simplify considerably and the coefficients are recognizable constants. The constant terms of the asymptotics are either ζ(p)(±q)\zeta^{(p)}(\pm q) (first two sums), 0 (third sum) or yield novel mathematical constants (fourth sum). This allows numerical computation of ζ(p)(±q)\zeta^{(p)}(\pm q) faster than any current software. One of the constants also appears in the expansion of the function n2(nlogn)s\sum_{n\geq 2} (n\log n)^{-s} around the singularity at s=1s=1; this requires the asymptotics of the incomplete gamma function. The manipulations involve polylogs for which we find a representation in terms of Nielsen integrals, as well as mysterious conjectures for Bernoulli numbers. Applications include the determination of the asymptotic growth of the Taylor coefficients of (z/log(1z))k(-z/\log(1-z))^k. We also give the asymptotics of Stirling numbers of first kind and their formula in terms of harmonic numbers.

Keywords

Cite

@article{arxiv.math/0607514,
  title  = {On asymptotics, Stirling numbers, Gamma function and polylogs},
  author = {Daniel B. Grünberg},
  journal= {arXiv preprint arXiv:math/0607514},
  year   = {2007}
}

Comments

24 pages, to appear in Results for Mathematics