Planar Turán Number of intersecting triangles

Abstract

The planar Turán number of a given graph $H$, denoted by $e{x}_{\mathcal{P}}(n,H)$, is the maximum number of edges over all planar graphs on $n$ vertices that do not contain a copy of $H$ as a subgraph. Let $H_k$ be a friendship graph, which is obtained from $k$ triangles by sharing a common vertex. In this paper, we obtain sharp bounds of $e{x}_{\mathcal{P}}(n,H_k)$ and $e{x}_{\mathcal{P}}(n,K_1+P_{k+1})$ for $k\ge 2$, which improves the results of Lan and Shi in Electron. J. Combin. 26 (2) (2019), \#P2.11.