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 A098182 #14 Jul 08 2025 12:17:17
%S A098182 1,1,3,9,25,69,191,529,1465,4057,11235,31113,86161,238605,660767,
%T A098182 1829857,5067409,14033137,38861859,107619849,298030825,825334485,
%U A098182 2285592479,6329473777,17528163337,48540608713,134423136579
%N A098182 a(n) = 3*a(n-1) - a(n-2) + a(n-3), a(0)=1,a(1)=1,a(2)=3.
%H A098182 G. C. Greubel, <a href="/A098182/b098182.txt">Table of n, a(n) for n = 0..1000</a>
%H A098182 Olivier Carton, Jean-Michel Couvreur, Martin Delacourt, and Nicolas Ollinger, <a href="https://doi.org/10.1007/978-3-031-97548-6_7">Linear Recurrence Sequence Automata and the Addition of Abstract Numeration Systems</a>, 15th Int'l Conf. Comb. Words (WORDS 2025) Lecture Notes Comp. Sci. (LNCS Vol. 15729) 70-82. See p. 71.
%H A098182 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-1,1).
%F A098182 G.f. : (1-x)^2/(1-3*x+x^2-x^3).
%F A098182 a(n) = Sum_{k=0..floor(n/2)} binomial(n+k, 3*k) * 2^k.
%t A098182 CoefficientList[Series[(1 - x)^2/(1 - 3 x + x^2 - x^3), {x,0,50}], x] (* _G. C. Greubel_, Mar 03 2017 *)
%o A098182 (PARI) my(x='x+O(x^50)); Vec((1-x)^2/(1-3*x+x^2-x^3)) \\ _G. C. Greubel_, Mar 03 2017
%Y A098182 Cf. A098183, A098184.
%K A098182 easy,nonn
%O A098182 0,3
%A A098182 _Paul Barry_, Aug 30 2004