The R-graph has 6 vertices. 4 vertices form a cycle and both the other two vertices are adjacent to a single one of those 4.
Table of n, a(n) for n=1..11.
F. Hüffner, tinygraph, software for generating integer sequences based on graph properties, version e8699da.
Cf. A079570, the same for the cricket graph (like an R-graph, but with a triangle instead of a 4-cycle).
Sequence in context: A130275 A156808 A245882 * A245880 A076324 A303032
Adjacent sequences: A267650 A267651 A267652 * A267654 A267655 A267656
Falk Hüffner, Jan 19 2016