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 A130977 #24 Jun 05 2021 02:23:09
%S A130977 1,6,66,876,12786,197796,3183156,52718616,892401426,15368638836,
%T A130977 268388185596,4741271556456,84573471344916,1521119577791976,
%U A130977 27554494253636136,502257203287150896,9205363627419463506
%N A130977 G.f.: 5/(2 + 3*sqrt(1-20*x)).
%C A130977 Number of walks of length 2n on the 6-regular tree beginning and ending at some fixed vertex. Hankel transform is A135349. - _Philippe Deléham_, Feb 25 2009
%H A130977 Vincenzo Librandi, <a href="/A130977/b130977.txt">Table of n, a(n) for n = 0..200</a>
%F A130977 a(n) = Sum_{k=0..n} A039599(n,k)*5^(n-k). - _Philippe Deléham_, Aug 25 2007
%F A130977 From _Gary W. Adamson_, Jul 22 2011: (Start)
%F A130977 a(n) = upper left term in M^n, M = an infinite square production matrix as follows:
%F A130977 6, 6, 0, 0, 0, 0, ...
%F A130977 5, 5, 5, 0, 0, 0, ...
%F A130977 5, 5, 5, 5, 0, 0, ...
%F A130977 5, 5, 5, 5, 5, 0, ...
%F A130977 5, 5, 5, 5, 5, 5, ...
%F A130977 ... (End)
%F A130977 D-finite with recurrence: n*a(n) = 2*(28*n-15)*a(n-1) - 360*(2*n-3)*a(n-2). - _Vaclav Kotesovec_, Oct 20 2012
%F A130977 a(n) ~ 3*2^(2*n-3)*5^(n+1)/(sqrt(Pi)*n^(3/2)). - _Vaclav Kotesovec_, Oct 20 2012
%t A130977 CoefficientList[Series[5/(2+3*Sqrt[1-20*x]), {x, 0, 20}], x] (* _Vaclav Kotesovec_, Oct 20 2012 *)
%Y A130977 Column k=6 of A183135.
%K A130977 nonn
%O A130977 0,2
%A A130977 _Philippe Deléham_, Aug 23 2007
%E A130977 More terms from _Olivier Gérard_, Sep 22 2007