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 A134813 #8 Mar 22 2018 17:28:11
%S A134813 1,-3,3,0,-6,12,-12,0,24,-48,48,0,-96,192,-192,0,384,-768,768,0,-1536,
%T A134813 3072,-3072,0,6144,-12288,12288,0,-24576,49152,-49152,0,98304,-196608,
%U A134813 196608,0,-393216,786432,-786432,0,1572864,-3145728,3145728,0,-6291456
%N A134813 a(n) = b(n+1)-2b(n) where b() is A134812.
%H A134813 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (-2,-2)
%F A134813 G.f. 1 -3*x*(1+x) / ( 1+2*x+2*x^2 ). - _R. J. Mathar_, Aug 11 2012
%F A134813 a(n) = -3*A009116(n-1), n>0. - _R. J. Mathar_, Aug 11 2012
%t A134813 LinearRecurrence[{-2,-2},{1,-3,3},50] (* _Harvey P. Dale_, Mar 22 2018 *)
%Y A134813 Cf. A003945.
%K A134813 sign
%O A134813 0,2
%A A134813 _Paul Curtz_, Jan 28 2008
%E A134813 More terms from _Harvey P. Dale_, Mar 22 2018