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 A137426 #6 Jul 31 2015 21:25:01
%S A137426 0,1,-3,3,-1,-5,11,-13,3,19,-45,51,-13,-77,179,-205,51,307,-717,819,
%T A137426 -205,-1229,2867,-3277,819,4915,-11469,13107,-3277,-19661,45875,
%U A137426 -52429,13107,78643,-183501,209715,-52429,-314573,734003,-838861,209715,1258291
%N A137426 a(n)=-a(n-1)+2a(n-3).
%H A137426 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (-1, 0, 2).
%F A137426 G.f.: (2*x^2-x)/(2*x^3-x-1). - _Harvey P. Dale_, Dec 03 2012
%t A137426 LinearRecurrence[{-1,0,2},{0,1,-3},80] (* _Harvey P. Dale_, Dec 03 2012 *)
%K A137426 sign
%O A137426 0,3
%A A137426 _Paul Curtz_, Apr 17 2008
%E A137426 More terms from _Harvey P. Dale_, Dec 03 2012