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 A075091 #10 Aug 31 2025 15:49:37
%S A075091 4,0,6,0,14,0,36,0,94,0,246,0,644,0,1686,0,4414,0,11556,0,30254,0,
%T A075091 79206,0,207364,0,542886,0,1421294,0,3720996,0,9741694,0,25504086,0,
%U A075091 66770564,0,174807606,0,457652254,0,1198149156,0,3136795214,0,8212236486,0,21499914244,0
%N A075091 Sum of Lucas numbers and reflected Lucas numbers (comment to A061084).
%C A075091 a(n) = ((-1)^n + 1)*L(n), where L(n) denotes the n-th Lucas number.
%H A075091 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,3,0,-1).
%F A075091 a(n) = 3*a(n-2) - a(n-4), a(0)=4, a(1)=0, a(2)=6, a(3)=0.
%F A075091 G.f.: (4 - 6x^2)/(1 - 3*x^2 + x^4).
%F A075091 E.g.f.: 4*cosh(x/2)*cosh(sqrt(5)*x/2). - _Stefano Spezia_, Aug 30 2025
%t A075091 CoefficientList[Series[(4 - 6*x^2)/(1 - 3*x^2 + x^4), {x, 0, 50}], x]
%t A075091 LinearRecurrence[{0,3,0,-1},{4,0,6,0},50] (* or *) Riffle[ LinearRecurrence[ {3,-1},{4,6},30],0] (* _Harvey P. Dale_, Aug 17 2018 *)
%Y A075091 Cf. A000032, A061084.
%K A075091 easy,nonn,changed
%O A075091 0,1
%A A075091 Mario Catalani (mario.catalani(AT)unito.it), Aug 31 2002
%E A075091 a(46)-a(49) from _Stefano Spezia_, Aug 30 2025