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 A111966 #13 Jan 30 2020 21:29:15
%S A111966 1,4,18,86,424,2128,10798,55190,283510,1461730,7557166,39153338,
%T A111966 203188892,1055863564,5492668906,28598497610,149012237696,
%U A111966 776904940576,4052654604042,21149661562298,110415949871240,576636302495488
%N A111966 Expansion of 1/(sqrt(1-6x+5x^2)-x).
%C A111966 Row sums of number triangle A111965.
%H A111966 Vincenzo Librandi, <a href="/A111966/b111966.txt">Table of n, a(n) for n = 0..300</a>
%F A111966 a(n) = Sum_{k=0..n} Sum_{j=0..n} C((k+2j-1)/2,j)*C(j,n-j-k)*(-6)^(k-n+2*j) * 5^(n-k-j).
%F A111966 D-finite with recurrence: n*a(n) = 3*(4*n-3)*a(n-1) - 3*(15*n-23)*a(n-2) + 18*(3*n-7) * a(n-3) - 20*(n-3)*a(n-4). - _Vaclav Kotesovec_, Oct 24 2012
%F A111966 a(n) ~ (sqrt(5)+3)^n/sqrt(5). - _Vaclav Kotesovec_, Oct 24 2012
%t A111966 CoefficientList[Series[1/(Sqrt[1-6*x+5*x^2]-x), {x, 0, 20}], x] (* _Vaclav Kotesovec_, Oct 24 2012 *)
%K A111966 easy,nonn
%O A111966 0,2
%A A111966 _Paul Barry_, Aug 23 2005