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 A134270 #7 Jul 31 2015 21:11:57
%S A134270 1,1,3,7,13,29,59,119,245,493,995,2007,4029,8093,16235,32535,65189,
%T A134270 130541,261331,523063,1046701,2094301,4189979,8382007,16767189,
%U A134270 33539181,67085635,134182423,268381725,536789149,1073617483,2147294423,4294679429,8589496685
%N A134270 a(n)=2a(n-1)+a(n-2)-4a(n-4).
%H A134270 Harvey P. Dale, <a href="/A134270/b134270.txt">Table of n, a(n) for n = 0..1000</a>
%H A134270 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2, 1, 0, -4).
%F A134270 O.g.f.: (1+x)*x/(2*x^3+x^2-1)-1/(2*x-1) . a(n) = -|A078028(n-1)| + 2^n . - _R. J. Mathar_, Feb 01 2008
%t A134270 LinearRecurrence[{2,1,0,-4},{1,1,3,7},40] (* _Harvey P. Dale_, Jan 16 2013 *)
%K A134270 nonn
%O A134270 0,3
%A A134270 _Paul Curtz_, Jan 30 2008
%E A134270 More terms from _Harvey P. Dale_, Jan 16 2013