Triangle-free;
Planar;
Number of colorings;
3-COLORINGS;
D O I:
10.1016/j.jctb.2022.05.003
中图分类号:
O1 [数学];
学科分类号:
0701 ;
070101 ;
摘要:
Thomassen conjectured that triangle-free planar graphs have exponentially many 3-colorings. Recently, he disproved his conjecture by providing examples of such graphs with n vertices and at most 215n/ log2 n 3-colorings. We improve his construction, giving examples of such graphs with at most 64(nlog9/2 3) < 64n(0.731 3)-colorings. We conjecture this exponent is optimal. (c) 2022 Elsevier Inc. All rights reserved.