The Ramsey Numbers of Large Star and Large Star-like Trees Versus Odd Wheels

Surahmat 1, Edy Tri Baskoro2, H. J. Broersma3
1Department of Mathematics Education, Universitas Islam Malang, Jalan MT Haryono 193 Malang 65144, Indonesia
2Department of Mathematics Institut Teknologi Bandung, Jalan Ganesa 10 Bandung, Indonesia
3 Faculty of Mathematical Sciences University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands,

Abstract

For two given graphs \( G \) and \( H \), the Ramsey number \( R(G, H) \) is the smallest positive integer \( N \) such that for every graph \( F \) of order \( N \) the following holds: either \( F \) contains \( G \) as a subgraph or the complement of \( F \) contains \( H \) as a subgraph. In this paper, we shall study the Ramsey number \( R(T_n, W_m) \) for a star-like tree \( T_n \) with \( n \) vertices and a wheel \( W_m \) with \( m + 1 \) vertices and \( m \) odd. We show that the Ramsey number \( R(S_n, W_m) = 3n – 2 \) for \( n \geq 2m – 4, m \geq 5 \) and \( m \) odd, where \( S_n \) denotes the star on \( n \) vertices. We conjecture that the Ramsey number is the same for general trees on \( n \) vertices, and support this conjecture by proving it for a number of star-like trees.

Keywords: Ramsey number, star, tree, wheel. AMS Subject Classifications: 05C55, 05D10.