Table of n, a(n) for n=1..9.
Wenchen He and Wenjie He, Generation and enumeration of planar polycyclic aromatic hydrocarbons, Tetrahedron 42.19 (1986): 5291-5299. See Table 1.
Cf. A003104, A323923-A323929.
A018190 is a very similar sequence with (as He and He remark) a slightly different definition.
Sequence in context: A111772 A233005 A018190 * A187982 A000228 A108070
Adjacent sequences: A323927 A323928 A323929 * A323931 A323932 A323933
N. J. A. Sloane, Feb 09 2019