%I #16 Sep 26 2019 03:42:37
%S 4,28,176,950,4908,24402,119240,575348,2757460,13157752,62638788,
%T 297832008,1415550920,6728600060,31998023632,152271569872,
%U 725231959452,3457304575812,16497751608120,78804354881238,376806016649964,1803539487096138,8641075826669256,41441524062045660
%N Number of polyhexes of class PF2.
%C See reference for precise definition.
%C Cyvin et al. has incorrect a(13) = 119204 and a(14) = 575312 due to using incorrect value for A039919(5); cf. A039659. - _Sean A. Irvine_, Sep 24 2019
%H S. J. Cyvin, Zhang Fuji, B. N. Cyvin, Guo Xiaofeng, and J. Brunvoll, <a href="https://doi.org/10.1021/ci00009a021">Enumeration and classification of benzenoid systems. 32. Normal perifusenes with two internal vertices</a>, J. Chem. Inform. Comput. Sci., 32 (1992), 532-540.
%F a(n + 4) = 3 * (N(n+2) - 6*N(n+1) + 8*N(n)) + A039919(floor((n+1)/2)) where N(n) = A002212(n) [from Cyvin]. - _Sean A. Irvine_, Sep 24 2019
%Y Cf. A026106, A026118, A030519, A030520, A030525, A030529, A030532, A030534, A002212, A039919.
%K nonn
%O 7,1
%A _N. J. A. Sloane_.
%E Corrected and extended by _Sean A. Irvine_, Sep 24 2019