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 A099432 #19 Sep 03 2019 03:36:42
%S A099432 1,6,33,162,756,3402,14931,64314,273051,1145988,4764744,19656756,
%T A099432 80561061,328316814,1331513397,5377120038,21633427836,86747114430,
%U A099432 346810621815,1382826606210,5500378861551,21830478128136,86469557676048
%N A099432 Convolution of A030195(n) (generalized (3,3)-Fibonacci) with itself.
%H A099432 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (6,-3,-18,-9).
%F A099432 G.f.: 1/(1 - 3*x - 3*x^2)^2.
%F A099432 a(n) = 6*a(n-1) - 3*a(n-2) - 18*a(n-3) - 9*a(n-4). [corrected by _Harvey P. Dale_, May 20 2011]
%F A099432 a(n) = Sum_{k=0..floor((n+2)/2)} k*binomial(n-k+2, k)*3^(n-k+1).
%F A099432 a(n) = (sqrt(7)*n + 2*sqrt(7) - sqrt(3))*(5*sqrt(7)/98 + sqrt(3)/14)*(3*sqrt(21)/2 + 15/2)^(n/2) + (15/2 - 3*sqrt(21)/2)^(n/2)*(sqrt(7)*n + 2*sqrt(7) + sqrt(3))*(5*sqrt(7)/98 - sqrt(3)/14)*(-1)^n.
%t A099432 LinearRecurrence[{6,-3,-18,-9},{1,6,33,162},30] (* _Harvey P. Dale_, May 20 2011 *)
%Y A099432 Cf. A073388.
%K A099432 easy,nonn
%O A099432 0,2
%A A099432 _Paul Barry_, Oct 15 2004