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 A097949 #21 Aug 20 2023 10:52:12
%S A097949 -2,1,-4,9,-34,121,-452,1681,-6274,23409,-87364,326041,-1216802,
%T A097949 4541161,-16947844,63250209,-236052994,880961761,-3287794052,
%U A097949 12270214441,-45793063714,170902040409,-637815097924,2380358351281,-8883618307202,33154114877521,-123732841202884
%N A097949 G.f.: -(2+7*x-x^3)/(1+4*x-4*x^3-x^4).
%C A097949 This is the sequence "ves(n)".
%H A097949 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (-4,0,4,1).
%F A097949 a(n) = -(-1)^n - (1/6)*( ( -sqrt(3) - 2 )^n + ( sqrt(3) - 2 )^n ) - 2/3. - _Eric Simon Jacob_, Aug 18 2023
%t A097949 CoefficientList[Series[-(2+7x-x^3)/(1+4x-4x^3-x^4),{x,0,40}],x] (* or *) LinearRecurrence[{-4,0,4,1},{-2,1,-4,9},40] (* _Harvey P. Dale_, Aug 11 2021 *)
%Y A097949 Cf. A001353, A097947, A097948.
%K A097949 sign
%O A097949 0,1
%A A097949 _N. J. A. Sloane_, following a suggestion of _Creighton Dement_, Sep 06 2004