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 A038390 #21 Jul 08 2025 22:23:58
%S A038390 1,2,5,11,17,27,42,57,78,106,134,170,215,260,315,381,447,525,616,707,
%T A038390 812,932,1052,1188,1341,1494,1665,1855,2045,2255,2486,2717,2970,3246,
%U A038390 3522,3822,4147,4472,4823,5201,5579,5985,6420,6855,7320,7816,8312,8840,9401
%N A038390 Bisection of A028289.
%H A038390 Vincenzo Librandi, <a href="/A038390/b038390.txt">Table of n, a(n) for n = 0..1000</a>
%H A038390 B. N. Cyvin et al., <a href="http://dx.doi.org/10.1007/BF02281733">Enumeration of conjugated hydrocarbons: Hollow hexagons revisited</a>, Structural Chem., 6 (1995), 85-88, equation (7).
%H A038390 <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1,2,-4,2,-1,2,-1).
%F A038390 G.f.: (x^3+2*x^2+1) / ((x-1)^4*(x^2+x+1)^2). - _Colin Barker_, Aug 30 2013
%F A038390 a(n) = (2*n^2+2+floor(n/3)*(10*floor(n/3)^2-(8*n-15)*floor(n/3)+2*n^2-8*n+7))/2. - _Luce ETIENNE_, Sep 14 2015
%t A038390 CoefficientList[Series[(x^3 + 2 x^2 + 1)/((x - 1)^4 (x^2 + x + 1)^2), {x, 0, 50}], x] (* _Vincenzo Librandi_, Oct 22 2013 *)
%K A038390 nonn,easy
%O A038390 0,2
%A A038390 _N. J. A. Sloane_
%E A038390 More terms from _Colin Barker_, Aug 30 2013