English

A tale of two omegas

Number Theory 2020-06-25 v3

Abstract

We consider ω(n)\omega(n) and Ω(n)\Omega(n), which respectively count the number of distinct and total prime factors of nn. We survey a number of similarities and differences between these two functions, and study the summatory functions L(x)=nx(1)Ω(n)L(x)=\sum_{n\leq x} (-1)^{\Omega(n)} and H(x)=nx(1)ω(n)H(x)=\sum_{n\leq x} (-1)^{\omega(n)} in particular. Questions about oscillations in both of these functions are connected to the Riemann hypothesis and other questions concerning the Riemann zeta function. We show that even though ω(n)\omega(n) and Ω(n)\Omega(n) have the same parity approximately 73.5\% of the time, these summatory functions exhibit quite different behaviors: L(x)L(x) is biased toward negative values, while H(x)H(x) is unbiased. We also prove that H(x)>1.7xH(x)>1.7\sqrt{x} for infinitely many integers xx, and H(x)<1.7xH(x)<-1.7\sqrt{x} infinitely often as well. These statements complement results on oscillations for L(x)L(x).

Keywords

Cite

@article{arxiv.1906.02847,
  title  = {A tale of two omegas},
  author = {Michael J. Mossinghoff and Timothy S. Trudgian},
  journal= {arXiv preprint arXiv:1906.02847},
  year   = {2020}
}

Comments

22 pages, submitted: v2 slightly revised

R2 v1 2026-06-23T09:46:20.890Z