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 A113142 #14 May 10 2024 10:58:52
%S A113142 0,1,-5,10,-14,18,-22,26,-30,34,-38,42,-46,50,-54,58,-62,66,-70,74,
%T A113142 -78,82,-86,90,-94,98,-102,106,-110,114,-118,122,-126,130,-134,138,
%U A113142 -142,146,-150,154,-158,162,-166,170,-174,178,-182,186
%N A113142 Expansion of x(1-3x+x^2+x^3)/(1+x)^2.
%C A113142 Second column in number triangle A113141.
%H A113142 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (-2,-1).
%F A113142 a(n) = -(-1)^n*(4n-2-C(1, n-1)+2*C(0, n)).
%t A113142 CoefficientList[Series[(x(1-3x+x^2+x^3))/(1+x)^2,{x,0,100}],x] (* or *) LinearRecurrence[{-2,-1},{0,1,-5,10,-14},100] (* _Harvey P. Dale_, Mar 23 2021 *)
%K A113142 easy,sign
%O A113142 0,3
%A A113142 _Paul Barry_, Oct 15 2005