English

Sums of element orders in groups of odd order

Group Theory 2019-05-30 v1

Abstract

Denote by GG a finite group and by ψ(G)\psi(G) the sum of element orders in GG. If tt is a positive integer, denote by CtC_t the cyclic group of order tt and write ψ(t)=ψ(Ct)\psi(t)=\psi(C_t). In this paper we proved the following Theorem A: Let GG be a non-cyclic group of odd order n=qmn=qm, where qq is the smallest prime divisor of nn and (m,q)=1(m,q)=1. Then the following statements hold. (1) If q=3q=3, then ψ(G)ψ(G)85301\frac {\psi(G)}{\psi(|G|)}\leq \frac {85}{301}, and equality holds if and only if n=37m1n=3\cdot 7\cdot m_1 with (m1,42)=1(m_1,42)=1 and G=(C7C3)×Cm1G=(C_7\rtimes C_3)\times C_{m_1}, with C7C3C_7\rtimes C_3 non-abelian. (2) If q>3q>3, then ψ(G)ψ(G)p4+p3p2+1p5+1\frac {\psi(G)}{\psi(|G|)}\leq \frac {p^4+p^3-p^2+1}{p^5+1}, where pp is the smallest prime bigger than qq and equality holds if and only if n=qp2m1n=qp^2m_1 with (m1,p!)=1(m_1,p!)=1 and G=Cq×Cp×Cp×Cm1G=C_q\times C_p\times C_p \times C_{m_1}.

Keywords

Cite

@article{arxiv.1905.12291,
  title  = {Sums of element orders in groups of odd order},
  author = {Marcel Herzog and Patrizia Longobardi and Mercede Maj},
  journal= {arXiv preprint arXiv:1905.12291},
  year   = {2019}
}