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 A027107 #19 Sep 08 2022 08:44:49
%S A027107 1,6,20,62,188,566,1700,5102,15308,45926,137780,413342,1240028,
%T A027107 3720086,11160260,33480782,100442348,301327046,903981140,2711943422,
%U A027107 8135830268,24407490806,73222472420,219667417262,659002251788
%N A027107 a(n) = Sum_{k=0..2n} (k+1) * A027082(n, 2n-k).
%H A027107 Vincenzo Librandi, <a href="/A027107/b027107.txt">Table of n, a(n) for n = 0..1000</a>
%H A027107 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (4,-3).
%F A027107 For n>0, a(n) = 7*3^(n-1) - 1.
%F A027107 G.f.: (1+2*x-x^2)/(1-4*x+3*x^2). [_Bruno Berselli_, Mar 25 2013]
%F A027107 a(n) = 2*A237930(n-1), n>0. - _R. J. Mathar_, Jun 24 2020
%t A027107 Join[{1}, Table[7 3^(n-1) - 1, {n, 30}]] (* _Vincenzo Librandi_, Mar 24 2013 *)
%o A027107 (Magma) [1] cat [7*3^n-1: n in [0..30]]; // _Vincenzo Librandi_, Mar 24 2013
%K A027107 nonn,easy
%O A027107 0,2
%A A027107 _Clark Kimberling_