On the Ramsey number of a cycle and complete graphs

Péter Madarasi

Published 2020-03-28Version 1

In this paper, we prove that the multicolored Ramsey number $R(G_1,\dots,G_n,K_{n_1},\dots,K_{n_r})$ is at least $(\gamma-1)(\kappa-1)+1$ for arbitrary connected graphs $G_1,\dots,G_n$ and $n_1,\dots,n_r\in\mathbb{N}$, where $\gamma=R(G_1,\dots,G_n)$ and $\kappa=R(K_{n_1},\dots,K_{n_r})$. Erd\H{o}s at al. conjectured that $R(C_n,K_l)=(n-1)(l-1)+1$ for every $n\geq l\geq 3$ except for $n=l=3$. Nikiforov proved this conjecture for $n\geq 4l+2$. Using the above bound, we derive the following generalization of this result. $R(C_n,K_{n_1},\dots,K_{n_r})=(n-1)(\kappa-1)+1$, where $\kappa=R(K_{n_1},\dots,K_{n_r})$ and $n\geq 4\kappa+2$.