%I #7 Jul 22 2019 21:54:40

%S 1,5,20,54,123,239,428,706,1107,1653,2386,3332,4543,6049,7910,10162,

%T 12873,16083,19870,24278,29393,35265,41988,49616,58253,67957,78840,

%U 90966,104455,119375,135856,153970,173855,195589,219318,245124

%N Expansion of (1+3*x+9*x^2+12*x^3+11*x^4+3*x^5+x^6)/((1-x)^2*(1-x^2)^2*(1-x^3)).

%D R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 6.28(c), y_4.

%H <a href="/index/Rec#order_09">Index entries for linear recurrences with constant coefficients</a>, signature (2,1,-3,-1,1,3,-1,-2,1).

%t CoefficientList[Series[(1+3x+9x^2+12x^3+11x^4+3x^5+x^6)/((1-x)^2(1-x^2)^2(1-x^3)),{x,0,40}],x] (* _Harvey P. Dale_, Jun 04 2019 *)

%K nonn

%O 0,2

%A _N. J. A. Sloane_, Jul 05 2000