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 A168053 #21 Sep 08 2022 08:45:48
%S A168053 1,1,-1,-3,-3,-5,-7,-7,-9,-11,-11,-13,-15,-15,-17,-19,-19,-21,-23,-23,
%T A168053 -25,-27,-27,-29,-31,-31,-33,-35,-35,-37,-39,-39,-41,-43,-43,-45,-47,
%U A168053 -47,-49,-51,-51,-53,-55,-55,-57,-59,-59,-61,-63,-63,-65,-67,-67,-69
%N A168053 Expansion of (1-2*x^2-3*x^3)/((1-x)^2*(1+x+x^2)).
%H A168053 G. C. Greubel, <a href="/A168053/b168053.txt">Table of n, a(n) for n = 0..1000</a>
%H A168053 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,1,-1).
%F A168053 a(n) = -(n^9 -45n^8 +846n^7 -8610n^6 +51345n^5 -181125n^4 +361584n^3 -361260n^2 +137264n -6720)/6720.
%F A168053 a(n) = A168054(n)/2^n.
%t A168053 LinearRecurrence[{1,0,1,-1},{1,1,-1,-3},60] (* _Harvey P. Dale_, Jan 15 2015 *)
%t A168053 CoefficientList[Series[(1 - 2 x^2 - 3 x^3) / ((1 - x)^2 (1 + x + x^2)), {x, 0, 80}], x] (* _Vincenzo Librandi_, Jul 08 2016 *)
%o A168053 (Magma) m:=55; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!((1-2*x^2-3*x^3)/((1-x)^2*(1+x+x^2)))); // _Bruno Berselli_, May 31 2013
%Y A168053 Cf. A168054.
%K A168053 sign,easy
%O A168053 0,4
%A A168053 _Paul Barry_, Nov 17 2009