%I #10 Sep 21 2017 12:14:14

%S 1,1,3,13,45,153,517,1737,5829,19561,65637,220233,738949,2479401,

%T 8319141,27913225,93657285,314248425,1054398181,3537823689,

%U 11870464773,39828987049,133638255909,448396626825,1504505828677,5048070509673,16937798036325,56831417423689,190686534309765,639810795074601

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

%H A. Goupil, M.-E. Pellerin and J. de Wouters d'oplinter, <a href="http://arxiv.org/abs/1307.8432">Snake Polyominoes</a>, arXiv preprint arXiv:1307.8432, 2013

%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (4,-3,4,-4).

%t a[0] = a[1] = 1; a[2] = 3; a[3] = 13; a[4] = 45; a[n_] := a[n] = 3*a[n-1] + 4*a[n-3] + 6; Array[a, 30, 0] (* _Jean-François Alcover_, Sep 21 2017 *)

%K nonn

%O 0,3

%A _N. J. A. Sloane_, Nov 23 2013