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 A190870 #18 Dec 21 2015 13:13:22
%S A190870 0,1,11,99,847,7139,59895,501787,4201967,35182323,294562279,
%T A190870 2466173963,20647543455,172867150819,1447292702999,12117142414971,
%U A190870 101448127098703,849352264956371,7111016118348615,59535427472794603,498447347597071103,4173141419166300867
%N A190870 a(n) = 11*a(n-1) - 22*a(n-2), a(0)=0, a(1)=1.
%H A190870 G. C. Greubel, <a href="/A190870/b190870.txt">Table of n, a(n) for n = 0..1000</a>
%H A190870 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11, -22).
%F A190870 a(n) = ((11+sqrt(33))^n-(11-sqrt(33))^n)/(2^n*sqrt(33)).
%F A190870 E.g.f.: (2/sqrt(33))*exp(11*x/2)*sinh(sqrt(33)*x/2). - _G. C. Greubel_, Dec 18 2015
%F A190870 G.f.: x/(1-11*x+22*x^2). - _G. C. Greubel_, Dec 18 2015
%t A190870 LinearRecurrence[{11, -22}, {0, 1}, 50] (* _T. D. Noe_, May 23 2011 *)
%o A190870 (PARI) concat(0, Vec(x/(1-11*x+22*x^2) + O(x^100))) \\ _Altug Alkan_, Dec 18 2015
%Y A190870 Cf. A190871, A190872, A190873
%K A190870 nonn
%O A190870 0,3
%A A190870 _Rolf Pleisch_, May 22 2011
%E A190870 Extended by _T. D. Noe_, May 23 2011