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 A107387 #20 Sep 08 2022 08:45:18
%S A107387 0,1,1,2,3,7,16,41,105,274,715,1871,4896,12817,33553,87842,229971,
%T A107387 602071,1576240,4126649,10803705,28284466,74049691,193864607,
%U A107387 507544128,1328767777,3478759201,9107509826,23843770275,62423800999,163427632720,427859097161
%N A107387 Expansion of x*(1-2*x-x^2)/( (1-x)*(1+x)*(1-3*x+x^2)).
%C A107387 The real roots of the denominator function are x = +-1, A104457 and A132338.
%H A107387 Vincenzo Librandi, <a href="/A107387/b107387.txt">Table of n, a(n) for n = 0..1000</a>
%H A107387 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (3,0,-3,1).
%F A107387 a(n) = 1 + A001654(n-2).
%t A107387 LinearRecurrence[{3,0,-3,1},{0,1,1,2},50] (* _Vincenzo Librandi_, Aug 22 2012 *)
%t A107387 CoefficientList[Series[x (1-2x-x^2)/((1-x)(1+x)(1-3x+x^2)),{x,0,40}],x] (* _Harvey P. Dale_, May 31 2020 *)
%o A107387 (Magma) I:=[ 0,1,1,2]; [n le 4 select I[n] else 3*Self(n-1)-3*Self(n-3) +Self(n-4): n in [1..40]] // _Vincenzo Librandi_, Aug 22 2012
%K A107387 nonn,easy
%O A107387 0,4
%A A107387 _Roger L. Bagula_, May 24 2005, corrected Sep 04 2008
%E A107387 Replaced with a regular sequence by _R. J. Mathar_, Aug 31 2011