%I A059712
%S A059712 1,2,6,19,63,213,729,2513,8703,30232,105236,366849,1280131,4470354,
%T A059712 15619386,54595869,190891131,667590414,2335121082,8168950665,
%U A059712 28580354769,100000811433,349918126509,1224476796543,4285005630969
%N A059712 Number of stacked directed animals on the square lattice.
%C A059712 The generating function is simply derived from the generating function 
               for directed animals. A triangular lattice version exists.
%D A059712 M. Bousquet-Melou and A. Rechnitzer, Lattice animals and heaps of dimers, 
               Discrete Math. 258 (2002), no. 1-3, 235-274.
%H A059712 M. Bousquet-Melou and A. Rechnitzer, <a href="http://www.labri.fr/Perso/
               ~bousquet/Articles/Klarner/article.ps.gz">Lattice animals and heaps 
               of dimers</a>
%F A059712 G.f.: ((1-2x)(1-3x)-(1-4x)sqrt((1-3x)(1+x)))/(2x(2-7x))
%p A059712 gf := ((1-2*x)*(1-3*x)-(1-4*x)*sqrt((1-3*x)*(1+x)))/(2*x*(2-7*x)): s 
               := series(gf, x, 50): for i from 1 to 100 do printf(`%d,`,coeff(s,
               x,i)) od:
%Y A059712 Directed animals: A005773.
%Y A059712 Sequence in context: A071738 A026012 A120900 this_sequence A059713 A109262 
               A006724
%Y A059712 Adjacent sequences: A059709 A059710 A059711 this_sequence A059713 A059714 
               A059715
%K A059712 nonn
%O A059712 1,2
%A A059712 Mireille Bousquet-Melou (bousquet(AT)labri.u-bordeaux.fr), Feb 08 2001
%E A059712 More terms from James A. Sellers (sellersj(AT)math.psu.edu), Feb 09 2001