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 A094556 #18 Sep 26 2023 13:40:17
%S A094556 0,1,0,7,8,51,100,407,1008,3451,9500,30207,87208,268451,791700,
%T A094556 2402407,7152608,21567051,64482700,193885007,580781208,1744091251,
%U A094556 5228778500,15693326007,47065997008,141225953051,423621935100,1270977653407
%N A094556 Number of walks of length n between opposite vertices on a triangular prism.
%H A094556 Andrew Howroyd, <a href="/A094556/b094556.txt">Table of n, a(n) for n = 0..1000</a>
%H A094556 R. J. Mathar, <a href="/A102518/a102518.pdf">Counting Walks on Finite Graphs</a>, Nov 2020, Section 3.
%H A094556 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (2,5,-6).
%F A094556 G.f.: x*(1 - 2*x + 2*x^2)/((1 - x)*(1 + 2*x)*(1 - 3*x)).
%F A094556 a(n) = 3^n/6 - (-2)^n/3 - 1/6 + 0^n/3.
%F A094556 a(n) = 2*a(n-1) + 5*a(n-2) - 6*a(n-3) for n >= 4.
%F A094556 E.g.f.: exp(-x)*(2+exp(3*x))*sinh(x)/3. - _Stefano Spezia_, Sep 26 2023
%t A094556 LinearRecurrence[{2,5,-6},{0,1,0,7},30] (* or *) CoefficientList[ Series[ x (1-2x+2x^2)/((1-x)(1+2x)(1-3x)),{x,0,30}],x] (* _Harvey P. Dale_, Jul 13 2011 *)
%o A094556 (PARI) a(n) = if(n==0, 0, (3^n - 2*(-2)^n - 1)/6) \\ _Andrew Howroyd_, Jun 15 2021
%Y A094556 Cf. A094554, A094555.
%K A094556 easy,nonn
%O A094556 0,4
%A A094556 _Paul Barry_, May 11 2004