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 A054459 #17 Feb 06 2024 10:17:11
%S A054459 1,6,23,76,233,682,1935,5368,14641,39406,104935,276996,725849,1890258,
%T A054459 4896415,12624752,32419297,82951766,211573047,538086716,1364974409,
%U A054459 3454480250,8724052271,21989264232,55326056977,138975010110
%N A054459 A001333(n), n >= 1, convolved with itself.
%C A054459 a(n) = A054458(n+1,1) (second column of convolution triangle).
%D A054459 R. P. Grimaldi, Ternary strings with no consecutive 0's and no consecutive 1's, Congressus Numerantium, 205 (2011), 129-149. (The sequence t_n, also the sequence lev_{n-1}.)
%H A054459 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (4,-2,-4,-1).
%F A054459 a(n) = ((4*n+3)*LP(n)+(2*n+1)*LP(n-1))/4, n >= 1, with LP(n) = A001333(n+1), a(0) = 1.
%F A054459 G.f.: ((1+x)/(1-2*x-x^2))^2.
%F A054459 a(n) = 2*A006645(n+2) - A000129(n+1). - _R. J. Mathar_, Feb 05 2024
%t A054459 LinearRecurrence[{4, -2, -4, -1}, {1, 6, 23, 76}, 30] (* _Paolo Xausa_, Feb 06 2024 *)
%Y A054459 Cf. A054458, A001333, A002203.
%K A054459 easy,nonn
%O A054459 0,2
%A A054459 _Wolfdieter Lang_, Apr 26 2000