English

The prime-counting Copeland-Erd\H{o}s constant

Number Theory 2023-09-26 v1

Abstract

Let (a(n):nN)(a(n) : n \in \mathbb{N}) denote a sequence of nonnegative integers. Let 0.a(1)a(2)...0.a(1)a(2)... denote the real number obtained by concatenating the digit expansions, in a fixed base, of consecutive entries of (a(n):nN)(a(n) : n \in \mathbb{N}). Research on digit expansions of this form has mainly to do with the normality of 0.a(1)a(2)...0.a(1)a(2)... for a given base. Famously, the Copeland-Erd\H{o}s constant 0.2357111317...0.2357111317..., for the case whereby a(n)a(n) equals the nthn^{\text{th}} prime number pnp_{n}, is normal in base 10. However, it seems that the ``inverse'' construction given by concatenating the decimal digits of (π(n):nN)(\pi(n) : n \in \mathbb{N}), where π\pi denotes the prime-counting function, has not previously been considered. Exploring the distribution of sequences of digits in this new constant 0.0122...9101011...0.0122...9101011... would be comparatively difficult, since the number of times a fixed mNm \in \mathbb{N} appears in (π(n):nN)(\pi(n) : n \in \mathbb{N}) is equal to the prime gap gm=pm+1pmg_{m} = p_{m+1} - p_{m}, with the behaviour of prime gaps notoriously elusive. Using a combinatorial method due to Sz\"usz and Volkmann, we prove that Cram\'er's conjecture on prime gaps implies the normality of 0.a(1)a(2)...0.a(1)a(2)... in a given base g2g \geq 2, for a(n)=π(n)a(n) = \pi(n).

Keywords

Cite

@article{arxiv.2309.13520,
  title  = {The prime-counting Copeland-Erd\H{o}s constant},
  author = {John M. Campbell},
  journal= {arXiv preprint arXiv:2309.13520},
  year   = {2023}
}

Comments

Submitted for publication