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 A128543 #43 Sep 08 2022 08:45:30
%S A128543 1,6,18,48,120,288,672,1536,3456,7680,16896,36864,79872,172032,368640,
%T A128543 786432,1671168,3538944,7471104,15728640,33030144,69206016,144703488,
%U A128543 301989888,629145600,1308622848,2717908992,5637144576
%N A128543 a(n) = floor(2^(n-2)*3*n).
%C A128543 Also row sums of triangle A249111. - _Reinhard Zumkeller_, Nov 15 2014
%H A128543 Vincenzo Librandi, <a href="/A128543/b128543.txt">Table of n, a(n) for n = 1..1000</a>
%H A128543 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (4,-4).
%F A128543 Binomial transform of A007310 (assuming offset 0 in both sequences).
%F A128543 Row sums of triangle A134239. - _Gary W. Adamson_, Oct 14 2007
%F A128543 a(n) = 3*n*2^(n-2) for n>1. - _R. J. Mathar_, Oct 25 2011
%F A128543 From _Colin Barker_, Mar 22 2012: (Start)
%F A128543 a(n) = 4*a(n-1) - 4*a(n-2) for n>3.
%F A128543 G.f.: x*(1+2*x-2*x^2)/(1-2*x)^2. (End)
%t A128543 CoefficientList[Series[(1+2*x-2*x^2)/(1-2*x)^2,{x,0,40}],x] (* _Vincenzo Librandi_, Jun 28 2012 *)
%o A128543 (Magma) I:=[1, 6, 18]; [n le 3 select I[n] else 4*Self(n-1)-4*Self(n-2): n in [1..40]]; // _Vincenzo Librandi_, Jun 28 2012
%o A128543 (Haskell)
%o A128543 a128543 = sum . a134239_row . subtract 1
%o A128543 -- _Reinhard Zumkeller_, Nov 15 2014
%o A128543 (PARI) a(n)=3*n*2^n\4 \\ _Charles R Greathouse IV_, Oct 07 2015
%o A128543 (Sage) [1]+[3*n*2^(n-2) for n in (2..40)] # _G. C. Greubel_, Jul 11 2019
%o A128543 (GAP) Concatenation([1], List([2..40], n-> 3*n*2^(n-2))); # _G. C. Greubel_, Jul 11 2019
%Y A128543 Cf. A007310, A134239, A249111.
%K A128543 nonn,easy
%O A128543 1,2
%A A128543 _Gary W. Adamson_, Mar 10 2007
%E A128543 Definition corrected by _M. F. Hasler_, Nov 05 2014