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 A089979 #10 Apr 30 2017 02:58:53
%S A089979 1,4,16,68,288,1216,5136,21696,91648,387136,1635328,6907904,29180160,
%T A089979 123261952,520679424,2199438336,9290801152,39245922304,165781442560,
%U A089979 700288974848,2958139588608,12495684124672,52783892398080
%N A089979 Expansion of 1/(1-4x-4x^3).
%H A089979 G. C. Greubel, <a href="/A089979/b089979.txt">Table of n, a(n) for n = 0..1000</a>
%H A089979 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (4,0,4).
%F A089979 a(n) = Sum_{k=0..floor(n/2)} C(n-2*k, k)*4^(n-2*k).
%F A089979 a(n) = 4*a(n-1) + 4*a(n-3). - _G. C. Greubel_, Apr 29 2017
%t A089979 CoefficientList[Series[1/(1 - 4*x - 4*x^3), {x, 0, 50}], x] (* or *) LinearRecurrence[{4,0,4}, {1,4,16}, 50] (* _G. C. Greubel_, Apr 29 2017 *)
%o A089979 (PARI) x='x+O('x^50); Vec(1/(1 - 4*x - 4*x^3)) \\ _G. C. Greubel_, Apr 29 2017
%Y A089979 Cf. A052912, A000930, A089978.
%K A089979 easy,nonn
%O A089979 0,2
%A A089979 _Paul Barry_, Nov 18 2003