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 A115102 #43 Dec 28 2024 10:27:07
%S A115102 2,8,12,28,52,108,212,428,852,1708,3412,6828,13652,27308,54612,109228,
%T A115102 218452,436908,873812,1747628,3495252,6990508,13981012,27962028,
%U A115102 55924052,111848108,223696212,447392428,894784852,1789569708,3579139412,7158278828
%N A115102 a(0)=2, a(1)=8, a(n) = a(n-1) + 2*a(n-2).
%C A115102 Essentially 2 * A084214.
%H A115102 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (1,2).
%F A115102 From _R. J. Mathar_, Jun 14 2011: (Start)
%F A115102 G.f.: (2+6*x)/( (1+x)*(1-2*x) ).
%F A115102 a(n) = 2*A084214(n+1). (End)
%F A115102 a(n) = (4*(-1)^n + 5*2^n)/3. - _Harvey P. Dale_, Sep 02 2016
%t A115102 LinearRecurrence[{1,2},{2,8},40] (* or *) Table[(4(-1)^x+5*2^x)/3,{x,40}] (* _Harvey P. Dale_, Sep 02 2016 *)
%Y A115102 Cf. A084214.
%K A115102 nonn,easy,less
%O A115102 0,1
%A A115102 _Roger L. Bagula_, Mar 02 2006
%E A115102 Edited by _N. J. A. Sloane_, Dec 04 2006