This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A123357 #16 Apr 03 2020 07:52:53
%S A123357 1,6,40,272,1856,12672,86528,590848,4034560,27549696,188121088,
%T A123357 1284571136,8771600384,59896233984,408997068800,2792806678528,
%U A123357 19070476877824,130221361594368,889207077732352,6071885729103872,41461429210972160,283116347854946304,1933239349151793152
%N A123357 Kekulé numbers for certain benzenoids (see the Cyvin-Gutman book for details).
%H A123357 S. J. Cyvin and I. Gutman, <a href="https://doi.org/10.1007/978-3-662-00892-8_12">Kekulé structures in benzenoid hydrocarbons</a>, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988 (see p. 210, formula page 204).
%H A123357 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (8,-8).
%F A123357 G.f.: -(2*x-1) / (8*x^2-8*x+1). - _Colin Barker_, Aug 29 2013
%F A123357 a(n) = A057084(n)-2*A057084(n-1). - _R. J. Mathar_, Jul 26 2019
%p A123357 A123357 := proc(n)
%p A123357 option remember;
%p A123357 if n <= 1 then
%p A123357 op(n+1,[1,6]) ;
%p A123357 else
%p A123357 8*(procname(n-1)-procname(n-2)) ;
%p A123357 end if
%p A123357 end proc:
%p A123357 seq( A123357(n),n=0..30) ; # _R. J. Mathar_, Jul 26 2019
%t A123357 LinearRecurrence[{8, -8}, {1, 6}, 30] (* _Jean-François Alcover_, Apr 03 2020 *)
%K A123357 nonn,easy
%O A123357 0,2
%A A123357 _N. J. A. Sloane_, Oct 10 2006