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 A154251 #9 Sep 08 2016 14:52:46
%S A154251 1,2,11,29,65,137,281,569,1145,2297,4601,9209,18425,36857,73721,
%T A154251 147449,294905,589817,1179641,2359289,4718585,9437177,18874361,
%U A154251 37748729,75497465,150994937,301989881,603979769,1207959545,2415919097
%N A154251 Expansion of (1-x+7x^2)/((1-x)(1-2x)).
%C A154251 Binomial transform of 1,1,8,1,8,1,8,1,8,1,8,1,8,1,8,...
%H A154251 G. C. Greubel, <a href="/A154251/b154251.txt">Table of n, a(n) for n = 0..1000</a>
%H A154251 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (3,-2).
%F A154251 a(n) = 3*a(n-1) - 2*a(n-2), n>2, with a(0)=1, a(1)=2, a(2)=11.
%F A154251 a(n) = 9*2^(n-1) - 7, n>0, with a(0)=1.
%F A154251 a(n) = 2*a(n-1) + 7, n>1, with a(0)=1, a(1)=2.
%F A154251 From _G. C. Greubel_, Sep 08 2016: (Start)
%F A154251 a(n) = 9*2^(n-1) - 7 for n >= 1.
%F A154251 E.g.f.: (1/2)*(9*exp(2*x) - 14*exp(x) + 7). (End)
%t A154251 Join[{1},LinearRecurrence[{3,-2},{2,11}, 25]] (* or *) Join[{1},Table[9*2^(n-1) - 7, {n,1,25}]] (* _G. C. Greubel_, Sep 08 2016 *)
%o A154251 (PARI) Vec((1-x+7*x^2)/((1-x)*(1-2*x))+O(x^99)) \\ _Charles R Greathouse IV_, Sep 26 2012
%Y A154251 Cf.: A094373, A000079, A083329, A095121, A154117, A131128, A154118, A131130
%K A154251 nonn,easy
%O A154251 0,2
%A A154251 _Philippe Deléham_, Jan 05 2009