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%I #14 May 27 2022 11:38:51
%S 1,2,3,9,15,21,36,51,66,94,122,150,195,240,285,351,417,483,574,665,
%T 756,876,996,1116,1269,1422,1575,1765,1955,2145,2376,2607,2838,3114,
%U 3390,3666,3991,4316,4641,5019,5397,5775,6210,6645,7080,7576,8072,8568,9129,9690
%N G.f.: (1+3*x^3)/((1-x)^2*(1-x^3)^2).
%H G. Nebe, E. M. Rains and N. J. A. Sloane, <a href="http://neilsloane.com/doc/cliff2.html">Self-Dual Codes and Invariant Theory</a>, Springer, Berlin, 2006.
%H <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1,2,-4,2,-1,2,-1).
%F a(n) ~ 2/27*n^3. - _Ralf Stephan_, Apr 29 2014
%t CoefficientList[Series[(1+3x^3)/((1-x)^2(1-x^3)^2),{x,0,80}],x] (* or *) LinearRecurrence[ {2,-1,2,-4,2,-1,2,-1},{1,2,3,9,15,21,36,51},80] (* _Harvey P. Dale_, May 27 2022 *)
%K nonn
%O 0,2
%A _N. J. A. Sloane_, Mar 20 2004
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