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%I #10 Oct 23 2019 20:32:19
%S 3,9,20,40,77,145,270,500,923,1701,3132,5764,10605,19509,35886,66008,
%T 121411,223313,410740,755472,1389533,2555753,4700766,8646060,15902587,
%U 29249421,53798076,98950092,181997597,334745773,615693470
%N a(n) = A027113(n, n+2).
%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,0,-1).
%F G.f.: [3+3x+2x^2]/[(1-x)(1-x-x^2-x^3)].
%t CoefficientList[Series[(3+3x+2x^2)/((1-x)(1-x-x^2-x^3)),{x,0,40}],x] (* or *) LinearRecurrence[{2,0,0,-1},{3,9,20,40},40] (* _Harvey P. Dale_, Sep 26 2017 *)
%Y Equals A089068(n+2) - 3.
%K nonn
%O 2,1
%A _Clark Kimberling_