The LivingstoneGraph() command returns the Livingstone graph, a distance-transitive graph with 266 vertices and 198 edges.

$\mathrm{with}\left(\mathrm{GraphTheory}\right)\:$

$\mathrm{with}\left(\mathrm{SpecialGraphs}\right)\:$

$G≔\mathrm{LivingstoneGraph}\left(\right)$

$G≔\mathrm{Graph\; 1:\; an\; undirected\; unweighted\; graph\; with\; 266\; vertices\; and\; 198\; edge(s)}$

$\mathrm{ChromaticNumber}\left(G\right)$

$3$

"Livingstone graph", Wikipedia. http://en.wikipedia.org/wiki/Livingstone_graph

The GraphTheory[SpecialGraphs][LivingstoneGraph] command was introduced in Maple 2019.

For more information on Maple 2019 changes, see Updates in Maple 2019.