English

On Ramsey number of $K_{2,n}$ versus even cycles

Combinatorics 2026-05-08 v3

Abstract

For graphs GG and HH, the Ramsey number R(G,H)R(G,H) is the smallest integer NN such that every graph Γ\Gamma on NN vertices contains GG or its complement Γ\overline{\Gamma} contains HH as a subgraph. In graph Ramsey theory, the star-cycle Ramsey number is well-studied throughout the years. Whereas the Ramsey number of K2,nK_{2,n} versus cycle is challenging to determine due to increased structural complexity. In this article, we have obtained an exact value of the Ramsey number R(K2,n,Cm)R(K_{2,n}, C_{m}) for even m[n,2n4008]m\in [n, 2n-4008] and n4516n\geq 4516. In particular, we show that R(K1,n,Cm)=R(K2,n,Cm)R(K_{1,n}, C_{m})= R(K_{2,n}, C_{m}) for all even m[n,2n4008]m\in [n, 2n-4008] and n4516n\geq 4516. This leads to an interesting question: For fixed tt, does there exist n0(t)Nn_0(t)\in \mathbb{N} such that R(K1,n,Cm)=R(Kt,n,Cm)R(K_{1,n}, C_m)=R(K_{t,n}, C_m) for all nn0(t)n \geq n_0(t) and for a given range of even mm?

Keywords

Cite

@article{arxiv.2604.02086,
  title  = {On Ramsey number of $K_{2,n}$ versus even cycles},
  author = {Abisek Dewan and Sayan Gupta and Rajiv Mishra},
  journal= {arXiv preprint arXiv:2604.02086},
  year   = {2026}
}

Comments

17 Pages, 3 Figures