The Moore four-color graph is a 341-vertex planar graph due to E. F. Moore that is somewhat resistant to four-coloring by hand (Wagon 1999). It has 1017 edges and chromatic number 4.
The Moore four-color graph should not be confused with a Moore graph in the sense of a regular graph that is a cage graph.
The Moore four-color partial graph is a 341-vertex spanning subgraph of the Moore four-color graph obtained by deleting 31 edges. It is also planar and has chromatic number 4, but is easier to draw while still providing a useful test case for graph four-coloring.
The Moore four-color graph and Moore four-color partial graph will be implemented in a future version of the Wolfram Language as GraphData["MooreFourColorGraph"] and GraphData["MooreFourColorPartialGraph"], respectively.
