The Grabarchuk graph is the Euclidean distance graph obtained from the vertices of a 
grid graph when two vertices are considered
adjacent when the Euclidean distance between them is 3. Rather surprisingly, the
resulting graph is sextic.
The graph is named after Serhiy Grabarchuk, who communicated it to D. Knuth in 2018 (D. Knuth, pers. comm., Jul. 11, 2025).
The Grabarchuk graph will be implemented in a future version of the Wolfram Language as GraphData["GrabarchukGraph"].
