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 A105811 #22 Dec 29 2024 08:50:55
%S A105811 1,-1,0,1,-2,3,-4,5,-6,7,-8,9,-10,11,-12,13,-14,15,-16,17,-18,19,-20,
%T A105811 21,-22,23,-24,25,-26,27,-28,29,-30,31,-32,33,-34,35,-36,37,-38,39,
%U A105811 -40,41,-42,43,-44,45,-46,47,-48,49,-50,51,-52,53,-54,55,-56,57,-58,59,-60,61,-62,63,-64,65
%N A105811 Expansion of g.f. (1+x-x^2)/(1+x)^2.
%C A105811 First column of number triangle A105810.
%H A105811 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (-2,-1).
%F A105811 a(n) = -0^n-(-1)^n*(n-2).
%F A105811 E.g.f.: exp(-x)*(2 + x) - 1. - _Stefano Spezia_, Dec 29 2024
%t A105811 CoefficientList[Series[(1+x-x^2)/(1+x)^2,{x,0,70}],x] (* or *) LinearRecurrence[ {-2,-1},{1,-1,0},70] (* _Harvey P. Dale_, Jun 16 2016 *)
%o A105811 (PARI) a(n)=-0^n-(-1)^n*(n-2) \\ _Charles R Greathouse IV_, Sep 02 2015
%Y A105811 Cf. A105810.
%K A105811 easy,sign
%O A105811 0,5
%A A105811 _Paul Barry_, May 04 2005