English

Essential $\mathcal{F}$-sets of $\mathbb{N}$ under nonhomogeneous spectra

Combinatorics 2024-05-01 v2

Abstract

Let α>0\alpha>0 and 0<γ<10<\gamma<1. Define gα,γ:NNg_{\alpha,\gamma}:\mathbb{N}\rightarrow\mathbb{N} by gα,γ(n)=αn+γg_{\alpha,\gamma}\left(n\right)=\lfloor\alpha n+\gamma\rfloor. The set {gα,γ(n):nN}\left\{ g_{\alpha,\gamma}\left(n\right):n\in\mathbb{N}\right\} is called the nonhomogeneous spectrum of α\alpha and γ\gamma. We refer to the maps gα,γg_{\alpha,\gamma} as nonhomogeneous spectra. In \cite{BHK}, Bergelson, Hindman and Kra showed that if AA is an IPIP-set, a central set, an IPIP^{\star}-set, or a central^{\star}-set, then gα,γ[A]g_{\alpha,\gamma}\left[A\right] is the corresponding objects. Hindman and Johnsons extended this result to include several other notions of largeness: CC-sets, JJ-sets, strongly central sets, piecwise syndetic sets, APAP-sets syndetic set, CC^{\star}-sets, strongly central^{\star}- sets . In \cite{DHS}, De, Hindman and Strauss introduced CC-set and JJ-set and showed that CC-sets satisfy the conclusion of the Central Sets Theorem. To prepare this article, we have been strongly motivated by the fact that CC-sets are essential J\mathcal{J}-sets. In this article, we prove some new results regarding nonhomogeneous spectra of essential F\mathcal{F}-sets for shift invariant F\mathcal{F}-sets. We have a special interest in the family HSD={AN:nA1n=}\mathcal{HSD}=\left\{ A\subseteq\mathbb{N}:\sum_{n\in A}\frac{1}{n}=\infty\right\} as this family is directly connected with the famous Erd\H{o}s sum of reciprocal conjecture and as a consequence we get gα,γ[P]HSDg_{\alpha,\gamma}\left[\mathbb{P}\right]\in\mathcal{HSD}, where P\mathbb{P} is the set of prime numbers in N\mathbb{N}. Throughout this article, we use some elementary techniques and algebra of the Stone-\v{C}ech compactifications of discrete semigroups.

Keywords

Cite

@article{arxiv.2212.10951,
  title  = {Essential $\mathcal{F}$-sets of $\mathbb{N}$ under nonhomogeneous spectra},
  author = {Pintu Debnath},
  journal= {arXiv preprint arXiv:2212.10951},
  year   = {2024}
}

Comments

15 pages. arXiv admin note: substantial text overlap with arXiv:2211.12372