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 A168589 #10 Sep 08 2022 08:45:49
%S A168589 1,1,-7,25,-79,241,-727,2185,-6559,19681,-59047,177145,-531439,
%T A168589 1594321,-4782967,14348905,-43046719,129140161,-387420487,1162261465,
%U A168589 -3486784399,10460353201,-31381059607,94143178825,-282429536479
%N A168589 a(n) = (2 - 3^n)*(-1)^n.
%C A168589 A signed version of A058481 preceded by 1.
%H A168589 Vincenzo Librandi, <a href="/A168589/b168589.txt">Table of n, a(n) for n = 0..200</a>
%H A168589 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (-4, -3).
%F A168589 a(n) = -4*a(n-1) - 3*a(n-2) for n > 1; a(0) = 1, a(1) = 1.
%F A168589 G.f.: (1 + 5*x)/((1+x)*(1+3*x)).
%F A168589 E.g.f.: 2*exp(-x) - exp(-3*x). - _G. C. Greubel_, Jul 26 2016
%t A168589 Table[(2 - 3^n)*(-1)^n, {n,0,50}] (* _G. C. Greubel_, Jul 26 2016 *)
%o A168589 (Magma) [ (2-3^n)*(-1)^n: n in [0..25] ];
%o A168589 (PARI) a(n)=(2-3^n)*(-1)^n \\ _Charles R Greathouse IV_, Jul 26 2016
%Y A168589 Cf. A058481 (3^n-2).
%K A168589 sign,easy
%O A168589 0,3
%A A168589 _Klaus Brockhaus_, Nov 30 2009