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 A121401 #23 Jul 10 2025 10:44:01
%S A121401 2,3,8,27,98,363,1352,5043,18818,70227,262088,978123,3650402,13623483,
%T A121401 50843528,189750627,708158978,2642885283,9863382152,36810643323,
%U A121401 137379191138,512706121227,1913445293768,7141075053843,26650854921602,99462344632563,371198523608648
%N A121401 a(n) = ((sqrt(3)+1)^n+(sqrt(3)-1)^n)^2/2^(n+1).
%H A121401 Stefano Spezia, <a href="/A121401/b121401.txt">Table of n, a(n) for n = 0..1700</a>
%H A121401 Yurii S. Bystryk, Vitalii L. Denysenko, and Volodymyr I. Ostryk, <a href="http://dx.doi.org/10.13140/RG.2.2.16511.73129">Lune and Lens Sequences</a>, ResearchGate preprint, 2024. See pp. 53, 56.
%H A121401 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (5,-5,1).
%F A121401 a(n) = ((2+sqrt(3))^n+(2-sqrt(3))^n)/2.
%F A121401 a(n) = A001075(n)+1.
%F A121401 From _R. J. Mathar_, Aug 07 2008: (Start)
%F A121401 a(n) = A102206(n-1).
%F A121401 G.f.: (1-3*x)*(x-2)/((x-1)*(x^2-4*x+1)). (End)
%F A121401 a(n) = 5*a(n-1) - 5*a(n-2) + a(n-3). - _Wesley Ivan Hurt_, Jan 16 2024
%F A121401 E.g.f.: cosh(x) + exp(2*x)*cosh(sqrt(3)*x) + sinh(x). - _Stefano Spezia_, Jul 09 2025
%t A121401 Table[((-1+Sqrt[3])^n+(1+Sqrt[3])^n)^2/(2^(n+1)),{n,0,25}]
%t A121401 LinearRecurrence[{5,-5,1},{2,3,8},25] (* _Ray Chandler_, Jan 27 2014 *)
%Y A121401 Cf. A001075, A102206.
%K A121401 nonn,easy
%O A121401 0,1
%A A121401 _Zak Seidov_, Sep 06 2006