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 A134271 #13 Oct 31 2019 07:47:18 %S A134271 0,1,2,0,4,4,4,12,12,20,36,44,76,116,164,268,396,596,932,1388,2124, %T A134271 3252,4900,7500,11404,17300,26404,40108,61004,92916,141220,214924, %U A134271 327052,497364,756900,1151468,1751628,2665268,4054564,6168524,9385100 %N A134271 a(n) = a(n-2) + 2*a(n-3), n > 3; with a(0)=0, a(1)=1, a(2)=2, a(3)=0. %C A134271 Recurrence in A052947. %H A134271 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (0,1,2). %F A134271 From _R. J. Mathar_, Feb 01 2008: (Start) %F A134271 O.g.f.: 1/2 + (1/2)*(-2*x-5*x^2+1)/(-1+x^2+2*x^3). %F A134271 a(n) = A052947(n-1) + 2*A052947(n-2) - A052947(n-3). (End) %Y A134271 Cf. A078050. %K A134271 nonn,easy %O A134271 0,3 %A A134271 _Paul Curtz_, Jan 30 2008