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 A073496 #14 Aug 22 2018 11:45:10
%S A073496 3,-1,-5,11,3,-41,43,83,-253,47,795,-1189,-1149,5511,-3253,-14429,
%T A073496 29699,10335,-113861,112555,239363,-690889,85355,2226675,-3173629,
%U A073496 -3421041,15168603,-8079109,-40847741,80253671,34210443,-315819197,293441539,688226495,-1884370309,113132363,6228205059
%N A073496 Expansion of (3 + 2*x + 3*x^2)/(1 + x + 3*x^2 - x^3).
%C A073496 Old name was "a(2n), where a(n) is A073145".
%H A073496 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (-1,-3,1)
%F A073496 G.f.: (3 + 2*x + 3*x^2)/(1 + x + 3*x^2 - x^3).
%F A073496 a(2n)=-a(2n-2)-3a(2n-4)+a(2n-6), a(0)=3, a(2)=-1, a(4)=-5.
%F A073496 Recurrence: a(n) = a(n-3) - 3a(n-2) - a(n-1), starting 3,-1,-5.
%t A073496 CoefficientList[Series[(3 + 2*x + 3*x^2)/(1 + x + 3*x^2 - x^3), {x, 0, 50}], x]
%t A073496 LinearRecurrence[{-1,-3,1},{3,-1,-5},40] (* _Harvey P. Dale_, Aug 22 2018 *)
%Y A073496 Bisection of A073145.
%K A073496 sign,easy
%O A073496 0,1
%A A073496 Mario Catalani (mario.catalani(AT)unito.it), Aug 03 2002