English

Maximizing weighted sums of binomial coefficients using generalized continued fractions

Number Theory 2024-05-30 v3

Abstract

Let m,rZm,r\in\mathbb{Z} and ωR\omega\in\mathbb{R} satisfy 0rm0\leqslant r\leqslant m and ω1\omega\geqslant1. Our main result is a generalized continued fraction for an expression involving the partial binomial sum sm(r)=i=0r(mi)s_m(r) = \sum_{i=0}^r\binom{m}{i}. We apply this to create new upper and lower bounds for sm(r)s_m(r) and thus for gω,m(r)=ωrsm(r)g_{\omega,m}(r)=\omega^{-r}s_m(r). We also bound an integer r0{0,1,,m}r_0 \in \{0,1,\dots,m\} such that gω,m(0)<<gω,m(r01)gω,m(r0)g_{\omega,m}(0)<\cdots<g_{\omega,m}(r_0-1)\leqslant g_{\omega,m}(r_0) and gω,m(r0)>>gω,m(m)g_{\omega,m}(r_0)>\cdots>g_{\omega,m}(m). For real ω3\omega\geqslant\sqrt3 we prove that r0{m+2ω+1,m+2ω+1+1}r_0\in\{\lfloor\frac{m+2}{\omega+1}\rfloor,\lfloor\frac{m+2}{\omega+1}\rfloor+1\}, and also r0=m+2ω+1r_0 =\lfloor\frac{m+2}{\omega+1}\rfloor for ω{3,4,}\omega\in\{3,4,\dots\} or ω=2\omega=2 and 3m3\nmid m.

Keywords

Cite

@article{arxiv.2310.12517,
  title  = {Maximizing weighted sums of binomial coefficients using generalized continued fractions},
  author = {S. P. Glasby and G. R. Paseman},
  journal= {arXiv preprint arXiv:2310.12517},
  year   = {2024}
}

Comments

14 pages, 1 figure, 1 table. Version 2 adds Remarks 4.9 and 5.4. To appear in Proc. Royal Soc. Edinburgh

R2 v1 2026-06-28T12:55:16.140Z