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 A087433 #17 Jul 11 2023 08:17:11
%S A087433 1,2,6,20,70,252,926,3460,13110,50252,194446,758100,2973350,11716252,
%T A087433 46333566,183739940,730176790,2906358252,11582386286,46200404980,
%U A087433 184414199430,736494536252,2942491360606,11759505089220,47006639297270
%N A087433 Expansion of g.f.: (1-2*x)*(1-4*x+x^2)/((1-x)*(1-3*x)*(1-4*x)).
%C A087433 Binomial transform of A087432. a(n+1) = 2*A085282(n).
%C A087433 Counts closed walks of length 2n at a vertex of the cyclic graph on 12 nodes C_12. - _Herbert Kociemba_, Jun 06 2004
%H A087433 Vincenzo Librandi, <a href="/A087433/b087433.txt">Table of n, a(n) for n = 0..1000</a>
%H A087433 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (8,-19,12).
%F A087433 G.f.: (1-2*x)*(1-4*x+x^2)/((1-x)*(1-3*x)*(1-4*x)).
%F A087433 a(n) = 0^n/6 + 1/3 + 3^n/3 + 4^n/6.
%F A087433 a(n) = 8*a(n-1) - 19*a(n-2) + 12*a(n-3). - _Wesley Ivan Hurt_, Jul 11 2023
%t A087433 CoefficientList[Series[(1-2x)(1-4x+x^2)/((1-x)(1-3x)(1-4x)),{x,0,30}],x] (* _Harvey P. Dale_, Nov 26 2014 *)
%o A087433 (Magma) [0^n/6+1/3+3^n/3+4^n/6: n in [0..30]]; // _Vincenzo Librandi_, Aug 12 2011
%Y A087433 Cf. A085282, A087432.
%K A087433 easy,nonn
%O A087433 0,2
%A A087433 _Paul Barry_, Sep 02 2003
%E A087433 Definition corrected by _Herbert Kociemba_, Jun 06 2004