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 A154118 #15 Sep 02 2016 22:52:58
%S A154118 1,2,9,23,51,107,219,443,891,1787,3579,7163,14331,28667,57339,114683,
%T A154118 229371,458747,917499,1835003,3670011,7340027,14680059,29360123,
%U A154118 58720251,117440507,234881019,469762043,939524091,1879048187,3758096379,7516192763,15032385531
%N A154118 Expansion of (1 - x + 5x^2)/((1-x)*(1-2x)).
%C A154118 Binomial transform of 1,1,6,1,6,1,6,1,6,1,6,1,6,1,6,...
%H A154118 G. C. Greubel, <a href="/A154118/b154118.txt">Table of n, a(n) for n = 0..1000</a>
%H A154118 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (3,-2).
%F A154118 a(n) = 7*2^(n-1) - 5, n>=1, with a(0)=1.
%F A154118 a(n) = 2*a(n-1) + 5, n>1, with a(0)=1, a(1)=2.
%F A154118 a(n) = 3*a(n-1) - 2*a(n-2), n>2, with a(0)=1, a(1)=2, a(2)=9.
%F A154118 E.g.f.: (1/2)*(5 - 10*exp(x) + 7*exp(2*x)). - _G. C. Greubel_, Sep 02 2016
%t A154118 Join[{1},Table[7*2^(n-1)-5,{n,15}]] (* _Vladimir Joseph Stephan Orlovsky_, Mar 14 2011*)
%t A154118 Join[{1, 2, 9}, LinearRecurrence[{3, -2}, {23, 51}, 20]] (* _G. C. Greubel_, Sep 02 2016 *)
%o A154118 (PARI) a(n)=if(n,7<<(n-1)-5,1) \\ _Charles R Greathouse IV_, Jan 17 2012
%K A154118 nonn,easy,less
%O A154118 0,2
%A A154118 _Philippe Deléham_, Jan 05 2009