English

The Ramsey Number $R(3,K_{10}-e)$ and Computational Bounds for $R(3,G)$

Combinatorics 2013-11-19 v2 Discrete Mathematics

Abstract

Using computer algorithms we establish that the Ramsey number R(3,K10e)R(3,K_{10}-e) is equal to 37, which solves the smallest open case for Ramsey numbers of this type. We also obtain new upper bounds for the cases of R(3,Kke)R(3,K_k-e) for 11k1611 \le k \le 16, and show by construction a new lower bound 55R(3,K13e)55 \le R(3,K_{13}-e). The new upper bounds on R(3,Kke)R(3,K_k-e) are obtained by using the values and lower bounds on e(3,Kle,n)e(3,K_l-e,n) for lkl \le k, where e(3,Kke,n)e(3,K_k-e,n) is the minimum number of edges in any triangle-free graph on nn vertices without KkeK_k-e in the complement. We complete the computation of the exact values of e(3,Kke,n)e(3,K_k-e,n) for all nn with k10k \leq 10 and for n34n \leq 34 with k=11k = 11, and establish many new lower bounds on e(3,Kke,n)e(3,K_k-e,n) for higher values of kk. Using the maximum triangle-free graph generation method, we determine two other previously unknown Ramsey numbers, namely R(3,K10K3e)=31R(3,K_{10}-K_3-e)=31 and R(3,K10P3e)=31R(3,K_{10}-P_3-e)=31. For graphs GG on 10 vertices, %besides G=K10G=K_{10}, this leaves 6 other open besides G=K10G=K_{10}, this leaves 6 open cases of the form R(3,G)R(3,G). The hardest among them appears to be G=K102K2G=K_{10}-2K_2, for which we establish the bounds 31R(3,K102K2)3331 \le R(3,K_{10}-2K_2) \le 33.

Keywords

Cite

@article{arxiv.1309.0038,
  title  = {The Ramsey Number $R(3,K_{10}-e)$ and Computational Bounds for $R(3,G)$},
  author = {Jan Goedgebeur and Stanisław P. Radziszowski},
  journal= {arXiv preprint arXiv:1309.0038},
  year   = {2013}
}

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25 pages