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 A027327 #20 Aug 13 2024 18:32:48
%S A027327 1,3,12,36,108,324,972,2916,8748,26244,78732,236196,708588,2125764,
%T A027327 6377292,19131876,57395628,172186884,516560652,1549681956,4649045868,
%U A027327 13947137604,41841412812,125524238436,376572715308
%N A027327 a(n) = Sum_{k=0..m} (k+1) * A026120(n, m-k), where m=0 for n=0,1; m=n for n >= 2.
%H A027327 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (3).
%F A027327 G.f.: (1+3x^2)/(1-3x). - _Paul Barry_, May 19 2003
%F A027327 a(n) = A003946(n), n>1. - _R. J. Mathar_, Oct 23 2008
%t A027327 Join[{1,3},NestList[3#&,12,30]] (* _Harvey P. Dale_, Aug 13 2024 *)
%K A027327 nonn
%O A027327 0,2
%A A027327 _Clark Kimberling_