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arXiv · 2212.12751

Planar Tur\'{a}n number of disjoint union of $C_3$ and $C_4$

Ping Li
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Abstract

The {\em planar Tur\'{a}n number} of $H$, denoted by $ex_{\mathcal{P}}(n,H)$, is the maximum number of edges in an $H$-free planar graph. The planar Tur\'{a}n number of $k\geq 3$ vertex-disjoint union of cycles is a trivial value $3n-6$. Lan, Shi and Song determine the exact value of $ex_{\mathcal{P}}(n,2C_3)$. We continue to study planar Tur\'{a}n number of vertex-disjoint union of cycles and obtain the exact value of $ex_{\mathcal{P}}(n,H)$, where $H$ is vertex-disjoint union of $C_3$ and $C_4$. The extremal graphs are also characterized. We also improve the lower bound of $ex_{\mathcal{P}}(n,2C_k)$ when $k$ is sufficiently large.

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Ping Li. 2022-12-24. Planar Tur\'{a}n number of disjoint union of $C_3$ and $C_4$. https://arxiv.org/abs/2212.12751

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