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 A165749 #17 Apr 07 2016 17:05:18
%S A165749 1,9,-63,585,-5247,47241,-425151,3826377,-34437375,309936393,
%T A165749 -2789427519,25104847689,-225943629183,2033492662665,-18301433963967,
%U A165749 164712905675721,-1482416151081471,13341745359733257
%N A165749 a(n) = (9/5)*(1+4*(-9)^(n-1)).
%H A165749 G. C. Greubel, <a href="/A165749/b165749.txt">Table of n, a(n) for n = 0..500</a>
%H A165749 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (-8, 9).
%F A165749 a(n) = -8*a(n-1) + 9*a(n-2), a(0)=1, a(1)=9.
%F A165749 a(n) = (-9)*a(n-1) + 18 for n>=1, with a(0)=1.
%F A165749 G.f.: (1+17x)/(1+8x-9x^2).
%F A165749 a(n) = Sum_{0<=k<=n} A112555(n,k)*8^(n-k).
%F A165749 E.g.f.: (1/5)*(9*exp(x) - 4*exp(-9*x)). - _G. C. Greubel_, Apr 07 2016
%t A165749 Table[9/5 (1+4(-9)^(n-1)),{n,0,20}] (* or *) LinearRecurrence[{-8,9},{1,9},20] (* _Harvey P. Dale_, Nov 24 2011 *)
%o A165749 (PARI) x='x+O('x^99); Vec((1+17*x)/(1+8*x-9*x^2)) \\ _Altug Alkan_, Apr 07 2016
%o A165749 (PARI) a(n) = (9-4*(-9)^n)/5 \\ _Charles R Greathouse IV_, Apr 07 2016
%K A165749 easy,sign
%O A165749 0,2
%A A165749 _Philippe Deléham_, Sep 26 2009