%I A006027 M1647
%S A006027 1,1,2,6,20,71,263,1005,3933,15684,63505,260390,1079019,4511700,
%T A006027 19011521,80653480,344193353,1476589475,6364258163,27545933212,
%U A006027 119676949397,521739175908,2281673067934,10006784399183
%N A006027 Number of directed column-convex polyominoes with perimeter 2n+2.
%D A006027 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A006027 M.-P. Delest, Utilisation des Langages Alg\'{e}briques et du Calcul Formel 
               Pour le Codage et l'Enumeration des Polyominos. Ph.D. Dissertation, 
               Universit\'{e} Bordeaux I, May 1987.
%D A006027 Delest, M.-P., Generating functions for column-convex polyominoes. J. 
               Combin. Theory Ser. A 48 (1988), no. 1, 12-31.
%D A006027 M.-P. Delest and S. Dulucq, Enumeration of directed column-convex animals 
               with given perimeter and area, Croat. Chem. Acta. 66 (1993), 59-80.
%D A006027 E. Duchi and S. Rinaldi, An object grammar for column-convex polyominoes, 
               Annals of Combinatorics, 8 (2004), 27-36.
%F A006027 G.f. A(x) = a(1)x^2 + a(2)x^3 + a(3)x^4 + ... satisfies the functional 
               equation A^3 + 2(x-1)A^2 + (2x-1)(x-1)A + (x^2)(x-1) = 0. - D. G. 
               Rogers, May 22 2005
%Y A006027 Cf. A005435.
%Y A006027 Sequence in context: A129777 A108600 A128729 this_sequence A049124 A163134 
               A150128
%Y A006027 Adjacent sequences: A006024 A006025 A006026 this_sequence A006028 A006029 
               A006030
%K A006027 nonn
%O A006027 1,3
%A A006027 Simon Plouffe (simon.plouffe(AT)gmail.com)
%E A006027 More terms from Douglas Rogers and Emanuele Munarini, May 15 2005