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 A098184 #34 Aug 29 2024 23:33:39
%S A098184 1,1,5,17,57,193,653,2209,7473,25281,85525,289329,978793,3311233,
%T A098184 11201821,37895489,128199521,433695873,1467182629,4963443281,
%U A098184 16791208345,56804250945,192167404461,650097672673,2199264673425
%N A098184 a(n) = 3a(n-1)+a(n-2)+a(n-3), a(0)=1, a(1)=1, a(2)=5.
%C A098184 Even bisection of the tribonacci sequence A000213. - _Oboifeng Dira_, Aug 03 2016
%H A098184 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,1,1).
%F A098184 G.f.: (1-x)^2/(1-3*x-x^2-x^3).
%F A098184 a(n) = Sum_{k=0..floor(n/2)} binomial(n+k, 3*k)*4^k.
%F A098184 a(n)/a(n-1) tends to 3.38297576..., the square of the tribonacci constant A058265. - _Gary W. Adamson_, Feb 28 2006
%t A098184 LinearRecurrence[{3,1,1},{1,1,5},30] (* _Harvey P. Dale_, Nov 29 2011 *)
%t A098184 CoefficientList[Series[(1 - x)^2/(1 - 3 x - x^2 - x^3), {x, 0, 24}], x] (* _Michael De Vlieger_, Aug 03 2016 *)
%o A098184 (Sage)
%o A098184 from sage.combinat.sloane_functions import recur_gen3
%o A098184 it = recur_gen3(1,1,1,3,1,1)
%o A098184 [next(it) for i in range(32)] # _Zerinvary Lajos_, Jun 24 2008
%o A098184 (PARI) a(n)=([0,1,0; 0,0,1; 1,1,3]^n*[1;1;5])[1,1] \\ _Charles R Greathouse IV_, Aug 03 2016
%Y A098184 Cf. A000213, A098182, A098183.
%K A098184 easy,nonn
%O A098184 0,3
%A A098184 _Paul Barry_, Aug 30 2004