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 A292290 #23 Apr 19 2019 11:45:37
%S A292290 0,0,3,6,12,27,66,168,435,1134,2964,7755,20298,53136,139107,364182,
%T A292290 953436,2496123,6534930,17108664,44791059,117264510,307002468,
%U A292290 803742891,2104226202,5508935712,14422580931,37758807078,98853840300,258802713819,677554301154
%N A292290 Number of vertices of type A at level n of the hyperbolic Pascal pyramid.
%H A292290 Colin Barker, <a href="/A292290/b292290.txt">Table of n, a(n) for n = 0..1000</a>
%H A292290 László Németh, <a href="http://arxiv.org/abs/1511.02067">Hyperbolic Pascal pyramid</a>, arXiv:1511.0267 [math.CO], 2015 (1st line of Table 1).
%H A292290 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (4,-4,1).
%F A292290 a(n) = 4*a(n-1) - 4*a(n-2) + a(n-3), n >= 4.
%F A292290 From _Colin Barker_, Sep 17 2017: (Start)
%F A292290 G.f.: 3*x^2*(1 - 2*x) / ((1 - x)*(1 - 3*x + x^2)).
%F A292290 a(n) = 3*(1 + (2^(-1-n)*((7-3*sqrt(5))*(3+sqrt(5))^n - (3-sqrt(5))^n*(7+3*sqrt(5)))) / sqrt(5)) for n>0.
%F A292290 (End)
%F A292290 a(n) = 3*(Fibonacci(2*n - 4) + 1) for n > 0. - _Ehren Metcalfe_, Apr 18 2019
%t A292290 CoefficientList[Series[3*x^2*(1 - 2*x)/((1 - x)*(1 - 3*x + x^2)), {x, 0, 30}], x] (* _Wesley Ivan Hurt_, Sep 17 2017 *)
%o A292290 (PARI) concat(vector(2), Vec(3*x^2*(1 - 2*x) / ((1 - x)*(1 - 3*x + x^2)) + O(x^30))) \\ _Colin Barker_, Sep 17 2017
%Y A292290 Cf. A264236.
%K A292290 nonn,easy
%O A292290 0,3
%A A292290 _Eric M. Schmidt_, Sep 13 2017