On a Relation between Schreier-type Sets and a Modification of Tur\'{a}n Graphs

TL;DR

This paper establishes a combinatorial connection between Schreier-type sets and a modified version of Turán graphs, generalizing previous relations and providing explicit formulas and sequence sums.

Contribution

It provides a combinatorial proof and generalization of the relation between Schreier-type sets and Turán graphs, extending the understanding of their structural connection.

Findings

Established that Sr(n, p, q) equals T(n+1, pq+1, q).

Proved Sr(n,p,q) is a partial sum of certain sequences.

Generalized the relation between Schreier-type sets and Turán graphs.

Abstract

Recently, a relation between Schreier-type sets and Tur\'{a}n graphs was discovered. In this note, we give a combinatorial proof and obtain a generalization of the relation. Specifically, for $p, q\ge 1$, let $$\mathcal{A}_q := \{F\subset\mathbb{N}: |F| = 1 \mbox{ or }F\mbox{ is an arithmetic progression with difference } q\}$$ and $$Sr(n, p, q)\ :=\ \#\{F\subset \{1, \ldots, n\}\,:\, p\min F\ge |F|\mbox{ and }F\in \mathcal{A}_q\}.$$ We show that $$Sr(n, p, q) \ =\ T(n+1, pq+1, q),$$ where $T(\cdot, \cdot, \cdot)$ is the number of edges of an $n$-vertex graph that is a modification of Tur\'{a}n graphs. We also prove that $Sr(n,p,q)$ is the partial sum of certain sequences.