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 A173559 #14 Jan 27 2019 15:28:25
%S A173559 1,-6,-13,-27,-50,-106,-208,-412,-840,-1656,-3328,-6672,-13280,-26656,
%T A173559 -53248,-106432,-213120,-425856,-851968,-1704192,-3407360,-6816256,
%U A173559 -13631488,-27261952,-54528000,-109049856,-218103808,-436211712,-872407040,-1744838656
%N A173559 a(n)= +2*a(n-2) +4*a(n-3), n>3.
%C A173559 Generated by scanning the diagonal of the table generated by A143025 in the top row followed by higher order differences in the other rows:
%C A173559 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8, 1, 8, 2, 8,...
%C A173559 7, -6, 6, -7, 7, -6, 6, -7, 7, -6, 6, -7, 7,...
%C A173559 -13, 12, -13, 14, -13, 12, -13, 14, -13, 12,..
%C A173559 25, -25, 27, -27, 25, -25, 27, -27, 25, -25,..
%C A173559 -50, 52, -54, 52, -50, 52, -54, 52, -50, 52, ...
%C A173559 102, -106, 106, -102, 102, -106, 106, -102,...
%H A173559 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (0,2,4).
%F A173559 a(n) = ( -13*2^n-2*A009116(n))/4, n>0.
%F A173559 a(n+1)-2*a(n) = -A137429(n-2), n>1.
%F A173559 G.f.: (6*x+15*x^2+19*x^3-1)/( (2*x-1) *(2*x^2+2*x+1)).
%t A173559 LinearRecurrence[{0,2,4},{1,-6,-13,-27},30] (* _Harvey P. Dale_, Jan 27 2019 *)
%K A173559 sign,easy
%O A173559 0,2
%A A173559 _Paul Curtz_, Feb 21 2010