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G.f.: -x*(1+x+x^2+2*x^3+3*x^4+3*x^5+x^6-x^7-x^9)/((1+x)*(-1+2*x+x^3)).
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%I #13 May 18 2020 11:32:11

%S 0,1,2,5,12,28,62,136,299,661,1456,3213,7085,15628,34467,76021,167668,

%T 369805,815629,1798928,3967659,8750949,19300824,42569309,93889565,

%U 207079956,456729219,1007348005,2221775964,4900281149,10807910301,23837596568,52575474283,115958858869

%N G.f.: -x*(1+x+x^2+2*x^3+3*x^4+3*x^5+x^6-x^7-x^9)/((1+x)*(-1+2*x+x^3)).

%D V. Vatter, The Enumeration and Structure of Permutation Classes, Ph. D. Dissertation, Rutgers Univ., Math. Dept., 2006.

%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (1,2,1,1).

%F a(n) = 2*a(n-1) + a(n-3) - 2*(-1)^n for n >= 10. - _Greg Dresden_, May 18 2020

%K nonn

%O 0,3

%A _N. J. A. Sloane_, Nov 17 2005