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 A348308 #18 Oct 12 2021 11:49:26
%S A348308 1,1,1,1,1,1,0,-3,-9,-19,-34,-55,-82,-112,-136,-135,-75,99,469,1147,
%T A348308 2269,3970,6325,9235,12231,14166,12771,4076,-18244,-63424,-143695,
%U A348308 -273223,-464779,-722439,-1027959,-1317915,-1448612,-1146827,52219,2870965,8337370,17769349,32615514,54022692,81938664
%N A348308 a(n) = Sum_{k=0..floor(n/6)} (-1)^k * binomial(n-3*k,3*k).
%H A348308 Seiichi Manyama, <a href="/A348308/b348308.txt">Table of n, a(n) for n = 0..1000</a>
%H A348308 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1,0,0,-1).
%F A348308 G.f.: (1-x)^2/((1-x)^3 + x^6).
%F A348308 a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) - a(n-6).
%t A348308 LinearRecurrence[{3, -3, 1, 0, 0, -1}, {1, 1, 1, 1, 1, 1}, 45] (* _Amiram Eldar_, Oct 11 2021 *)
%o A348308 (PARI) a(n) = sum(k=0, n\6, (-1)^k*binomial(n-3*k, 3*k));
%o A348308 (PARI) my(N=66, x='x+O('x^N)); Vec((1-x)^2/((1-x)^3+x^6))
%Y A348308 Cf. A348309, A348310.
%Y A348308 Cf. A057681, A100134.
%K A348308 sign
%O A348308 0,8
%A A348308 _Seiichi Manyama_, Oct 11 2021