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 A166035 #13 Apr 24 2016 15:16:48
%S A166035 1,-3,15,-51,231,-843,3615,-13731,57111,-221883,907215,-3569811,
%T A166035 14456391,-57294123,230770815,-918300291,3687550071,-14707153563,
%U A166035 58957754415,-235443597171,942936650151,-3768259816203,15083499618015
%N A166035 a(n) = (3^n+6*(-4)^n)/7.
%H A166035 G. C. Greubel, <a href="/A166035/b166035.txt">Table of n, a(n) for n = 0..1000</a>
%H A166035 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (-1,12).
%F A166035 a(n) = -a(n-1) + 12*a(n-2), a(0) = 1, a(1) = -3, for n>1.
%F A166035 a(n) = Sum_{0<=k<=n} A112555(n,k)*(-4)^k.
%F A166035 G.f.: (1-2x)/(1+x-12x^2).
%F A166035 E.g.f.: (1/7)*(exp(3*x) + 6*exp(-4*x)). - _G. C. Greubel_, Apr 24 2016
%t A166035 LinearRecurrence[{-1, 12}, {1, -3}, 100] (* _G. C. Greubel_, Apr 24 2016 *)
%o A166035 (PARI) a(n)= (3^n+6*(-4)^n)/7;
%o A166035 for(n=0,33,print1(a(n),", "));
%Y A166035 Cf. A077925, A091004.
%K A166035 easy,sign
%O A166035 0,2
%A A166035 _Philippe Deléham_, Oct 05 2009
%E A166035 a(5) corrected by _Tilman Neumann_, Dec 31 2010