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 A157128 #12 Oct 23 2019 07:10:27
%S A157128 1,-1,-1,-1,2,1,1,-3,-1,-1,4,1,1,-5,-1,-1,6,1,1,-7,-1,-1,8,1,1,-9,-1,
%T A157128 -1,10,1,1,-11,-1,-1,12,1,1,-13,-1,-1,14,1,1,-15,-1,-1,16,1,1,-17,-1,
%U A157128 -1,18,1,1,-19,-1,-1,20,1,1
%N A157128 Expansion of (1 - x - x^2 + x^3 - x^5) / ((1 + x)^2*(1 - x + x^2)^2).
%C A157128 Hankel transform of A157127.
%H A157128 Colin Barker, <a href="/A157128/b157128.txt">Table of n, a(n) for n = 0..1000</a>
%H A157128 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,-2,0,0,-1).
%F A157128 a(n) = -2*a(n-3) - a(n-6) for n>5. - _Colin Barker_, Oct 23 2019
%t A157128 CoefficientList[Series[(1-x-x^2+x^3-x^5)/(1+2x^3+x^6),{x,0,60}],x] (* or *) LinearRecurrence[{0,0,-2,0,0,-1},{1,-1,-1,-1,2,1},70] (* _Harvey P. Dale_, Jul 08 2019 *)
%o A157128 (PARI) Vec((1 - x - x^2 + x^3 - x^5) / ((1 + x)^2*(1 - x + x^2)^2) + O(x^80)) \\ _Colin Barker_, Oct 23 2019
%K A157128 easy,sign
%O A157128 0,5
%A A157128 _Paul Barry_, Feb 23 2009