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 A135139 #22 Sep 25 2024 23:13:08
%S A135139 1,2,4,12,24,68,144,388,856,2228,5056,12852,29736,74372,174384,431332,
%T A135139 1020664,2505428,5965984,14568468,34840776,84774308,203340816,
%U A135139 493553092,1186252696,2874447092,6918369664,16744740852,40340742504,97560443588
%N A135139 a(n) = 5*a(n-2) + 2*a(n-3).
%H A135139 Harvey P. Dale, <a href="/A135139/b135139.txt">Table of n, a(n) for n = 0..1000</a>
%H A135139 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (0, 5, 2).
%F A135139 From _R. J. Mathar_, Feb 15 2008: (Start)
%F A135139 O.g.f.: 4*(x-2)/(7*(x^2+2*x-1)) - 1/(7*(1+2*x)).
%F A135139 a(n) = (4*A078343(n+1)-(-2)^n)/7.
%F A135139 a(n) = A135138(n+2) + 2*A135138(n+1) - A135138(n). (End)
%t A135139 a = {1, 2, 4}; Do[AppendTo[a, 5*a[[ -2]] + 2*a[[ -3]]], {40}]; a (* _Stefan Steinerberger_, Feb 15 2008 *)
%t A135139 LinearRecurrence[{0,5,2},{1,2,4},30] (* _Harvey P. Dale_, May 25 2012 *)
%Y A135139 Cf. A135138.
%K A135139 nonn,easy
%O A135139 0,2
%A A135139 _Paul Curtz_, Feb 13 2008
%E A135139 More terms from _R. J. Mathar_ and _Stefan Steinerberger_, Feb 15 2008