Gallai-Ramsey number conjecture for the three-triangle fan

Let FnF_n be the fan graph with nn triangles, defined by

Fn=K1+nK2,F_n=K_1+n\overline{K_2},

so that F3F_3 is the fan with three triangles, and let grk(K3;F3)gr_k(K_3;F_3) denote the kk-color Gallai-Ramsey number of F3F_3 versus K3K_3. The authors' conjecture. For k2k\geq 2,

grk(K3;F3)={145k221,if k is even;335k32,if k is odd.gr_k(K_3;F_3)=\begin{cases} 14\cdot 5^{\frac{k-2}{2}}-1, & \text{if }k\text{ is even};\\ 33\cdot 5^{\frac{k-3}{2}}, & \text{if }k\text{ is odd}. \end{cases}

This asserts that the lower bound in the odd-kk case of the preceding theorem is sharp, completing the exact determination of the Gallai-Ramsey numbers for F3F_3. The even-kk case and the odd cases k=3,5k=3,5 are proved in the paper, while the general odd case is left open.

Sources & referencesView supporting material

Primary source

Yaping Mao, Zhao Wang, Colton Magnant and Ingo Schiermeyer, “Gallai-Ramsey numbers for fans”, arXiv:1902.10706 (2019).

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