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 A084247 #34 Apr 24 2023 02:04:09
%S A084247 1,2,0,4,-4,12,-20,44,-84,172,-340,684,-1364,2732,-5460,10924,-21844,
%T A084247 43692,-87380,174764,-349524,699052,-1398100,2796204,-5592404,
%U A084247 11184812,-22369620,44739244,-89478484,178956972,-357913940,715827884,-1431655764,2863311532
%N A084247 a(n) = -a(n-1) + 2*a(n-2), a(0)=1, a(1)=2.
%C A084247 Row sums of triangle in A112555. - _Philippe Deléham_, Sep 21 2009
%H A084247 Vincenzo Librandi, <a href="/A084247/b084247.txt">Table of n, a(n) for n = 0..1000</a>
%H A084247 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (-1,2).
%F A084247 Binomial transform of A084246.
%F A084247 a(n) = A077925(n-1) + 1.
%F A084247 a(n) = (4 - (-2)^n)/3.
%F A084247 G.f.: (1+3*x)/((1-x)*(1+2*x)).
%F A084247 E.g.f.: (4*exp(x) - exp(-2*x))/3.
%F A084247 a(n) = (-1)^(n+1)*(A078008(n+1) - A078008(n)). - _Paul Curtz_, Jun 30 2008, Feb 24 2021
%F A084247 a(n) = -2*a(n-1) + 4 . - _Philippe Deléham_, Sep 15 2009
%F A084247 a(n+1) = 2*A151575(n). - _Philippe Deléham_, Sep 21 2009
%F A084247 a(n) = A077925(n) + 3*A077925(n-1). - _R. J. Mathar_, Feb 24 2021
%t A084247 LinearRecurrence[{-1,2},{1,2},40] (* _Harvey P. Dale_, Nov 05 2016 *)
%o A084247 (Magma) [(4-(-2)^n)/3: n in [0..40]]; // _Vincenzo Librandi_, Aug 13 2011
%o A084247 (PARI) Vec((1+3*x)/((1-x)*(1+2*x)) + O(x^40)) \\ _Michel Marcus_, Feb 25 2016
%o A084247 (SageMath) [(4-(-2)^n)/3 for n in range(41)] # _G. C. Greubel_, Apr 24 2023
%Y A084247 Cf. A077925, A078008, A084246, A112555, A151575.
%K A084247 easy,sign
%O A084247 0,2
%A A084247 _Paul Barry_, May 23 2003