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arXiv · 2606.19717

Counting triangles in graphs with no wheels of order at least five

Chunyang Dou·Bo Ning·Xing Peng
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Abstract

For a family of graphs $\mathcal F$, a graph $G$ is said to be $\mathcal F$-free if it contains no member of $\mathcal F$ as a subgraph. A wheel graph $W_k$ is a graph on $k+1$ vertices formed by joining a new vertex to all vertices of a $k$-cycle. Given an integer $k\ge 3$, we consider the problem of determining the maximum number of triangles in a $W_{\geq k}$-free graph, where $W_{\geq k}=\{W_\ell: \ell \geq k\}$. The case $k=3$ was raised by Gallai, who proposed a conjecture for this case (see Erd\H{o}s [5]. Gallai's conjecture was disproved by Zhou [17] and independently by F\"uredi, Goemans, and Kleitman [9]. In this paper, we study the case $k=4$. Namely, for every integer $n\ge 3$, we determine the maximum number of triangles in an $n$-vertex $W_{\geq 4}$-free graph and characterize all extremal graphs.

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Chunyang Dou, Bo Ning, Xing Peng. 2026-06-18. Counting triangles in graphs with no wheels of order at least five. https://arxiv.org/abs/2606.19717

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