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 A105812 #21 Feb 17 2021 10:07:35
%S A105812 1,0,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,
%T A105812 -1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,
%U A105812 1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1
%N A105812 Expansion of (1+x-x^2)/(1+x).
%C A105812 Row sums of number triangle A105810.
%H A105812 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (-1).
%F A105812 a(n) = -(-1)^n-binomial(1, n)+3*binomial(0, n).
%F A105812 a(n) = A033999(n-1), n>1. - _R. J. Mathar_, Aug 28 2008
%F A105812 E.g.f.: 2 - x - exp(-x). - _Alejandro J. Becerra Jr._, Feb 17 2021
%t A105812 LinearRecurrence[{-1}, {1, 0, -1}, 78] (* _Ray Chandler_, Jul 30 2015 *)
%o A105812 (PARI) a(n)=if(n<2,1-n,-(-1)^n) \\ _Charles R Greathouse IV_, Jun 06 2013
%Y A105812 Cf. A033999, A105810.
%K A105812 easy,sign
%O A105812 0,1
%A A105812 _Paul Barry_, May 04 2005