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 A133310 #27 Sep 24 2024 02:51:00
%S A133310 1,2,1,3,4,3,5,6,5,7,8,7,9,10,9,11,12,11,13,14,13,15,16,15,17,18,17,
%T A133310 19,20,19,21,22,21,23,24,23,25,26,25,27,28,27,29,30,29,31,32,31,33,34,
%U A133310 33,35,36,35,37,38,37,39,40,39,41,42,41,43,44,43,45,46,45,47,48,47,49,50
%N A133310 a(3n) = 2n+1, a(3n+1) = 2n+2, a(3n+2) = 2n+1.
%H A133310 G. C. Greubel, <a href="/A133310/b133310.txt">Table of n, a(n) for n = 0..5000</a>
%H A133310 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,1,-1).
%F A133310 G.f.: ( 1+x-x^2+x^3 ) / ( (1+x+x^2)*(x-1)^2 ). - _R. J. Mathar_, May 23 2014
%F A133310 a(n) = (2/9)*(3*n+3+3*cos(2*(n-1)*Pi/3)-2*sqrt(3)*sin(2*(n-1)*Pi/3)). - _Wesley Ivan Hurt_, Sep 30 2017
%t A133310 CoefficientList[Series[(1+x-x^2+x^3)/((1+x+x^2)*(x-1)^2), {x, 0, 50}], x] (* _G. C. Greubel_, Feb 10 2018 *)
%t A133310 LinearRecurrence[{1, 0, 1, -1}, {1, 2, 1, 3}, 74] (* _Robert G. Wilson v_, Feb 10 2018 *)
%o A133310 (PARI) my(x='x+O('x^70)); Vec((1+x-x^2+x^3)/((1+x+x^2)*(x-1)^2)) \\ _G. C. Greubel_, Feb 10 2018
%o A133310 (Magma) Q:=Rationals(); R<x>:=PowerSeriesRing(Q, 70); Coefficients(R!((1+x-x^2+x^3)/((1+x+x^2)*(x-1)^2))) // _G. C. Greubel_, Feb 10 2018
%Y A133310 Cf. A130823 (1, 1, 1, 3, 3, 3).
%K A133310 nonn,easy
%O A133310 0,2
%A A133310 _Paul Curtz_, Oct 18 2007