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 A134812 #17 Apr 11 2025 10:32:36
%S A134812 0,1,-1,1,2,-2,8,4,8,40,32,112,224,352,896,1600,3200,6784,12800,26368,
%T A134812 52736,103936,210944,418816,837632,1681408,3350528,6713344,13426688,
%U A134812 26828800,53706752,107364352,214728704,429555712,858914816,1718026240,3436052480,6871711744,13744209920
%N A134812 a(n) = 2a(n-2) + 4a(n-3), n >= 3.
%H A134812 Joshua Zucker, <a href="/A134812/b134812.txt">Table of n, a(n) for n = 0..60</a>
%H A134812 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (0,2,4).
%F A134812 G.f.: x*(-1 + x + x^2) / ( (2*x-1)*(2*x^2 + 2*x + 1) ). - _R. J. Mathar_, Aug 11 2012
%F A134812 20*a(n) = 2^n - 6*A078069(n), n>0. - _R. J. Mathar_, Aug 11 2012
%t A134812 CoefficientList[Series[x*(-1 + x + x^2) / ( (2*x-1)*(2*x^2 + 2*x + 1) ),{x,0,38}],x] (* _James C. McMahon_, Apr 11 2025 *)
%Y A134812 Cf. A038521.
%K A134812 sign,easy
%O A134812 0,5
%A A134812 _Paul Curtz_, Jan 28 2008
%E A134812 More terms from _Joshua Zucker_, Feb 23 2008