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 A132158 #6 Sep 23 2015 15:40:52
%S A132158 0,1,3,6,11,15,24,49,75,126,251,375,624,1249,1875,3126,6251,9375
%N A132158 a(3n+k) = 3a(3n+k-1)-3a(3n+k-2)+2a(3n+k-3) for k = 0,1; a(3n+2) = 3a(3n-1)-3a(3n-2), with a(0) = 0,a(1) = 1,a(2) = 3.
%H A132158 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1, -1, 5, -5, 5).
%F A132158 Sequence is identical to its third differences in absolute values.
%F A132158 G.f.:-x*(x+1)*(3*x^2+x+1)/((x^2-x+1)*(5*x^3-1)) [From Maksym Voznyy (voznyy(AT)mail.ru), Aug 12 2009]
%t A132158 LinearRecurrence[{1, -1, 5, -5, 5},{0, 1, 3, 6, 11},18] (* _Ray Chandler_, Sep 23 2015 *)
%K A132158 nonn
%O A132158 0,3
%A A132158 _Paul Curtz_, Nov 02 2007