%I A001420 M0806 N0305
%S A001420 2,3,6,14,36,94,250,675,1838,5053,14016,39169,110194,311751,886160,
%T A001420 2529260,7244862,20818498,59994514,173338962,501994070,1456891547,
%U A001420 4236446214,12341035217,36009329450,105229462401,307942754342,902338712971,
               2647263986022,7775314024683,22861250676074
%N A001420 Number of fixed 2-dimensional triangular-celled animals with n cells 
               (n-iamonds) in the 2-dimensional hexagonal lattice.
%C A001420 The hexagonal lattice is the familiar 2-dimensional lattice in which 
               each point has 6 neighbors. This is sometimes called the triangular 
               lattice.
%D A001420 Gadi Aleksandrowicz and Gill Barequet, Counting d-Dimensional Polycubes 
               and Nonrectangular Polyominoes, in Computing and Combinatorics, Lecture 
               Notes in Computer Science, Volume 4112, 2006, pp. 418-427, Springer-Verlag. 
               [From N. J. A. Sloane, Jul 09 2009]
%D A001420 W. F. Lunnon, Counting hexagonal and triangular polyominoes, pp. 87-100 
               of R. C. Read, editor, Graph Theory and Computing. Academic Press, 
               NY, 1972.
%D A001420 D. H. Redelmeier, personal communication.
%D A001420 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A001420 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%H A001420 G. Nebe and N. J. A. Sloane, <a href="http://www.research.att.com/~njas/
               lattices/A2.html">Home page for hexagonal (or triangular) lattice 
               A2</a>
%Y A001420 Cf. A000577, A001168, A006534, A030223, A030224.
%Y A001420 Sequence in context: A002995 A093467 A080408 this_sequence A049339 A157100 
               A081293
%Y A001420 Adjacent sequences: A001417 A001418 A001419 this_sequence A001421 A001422 
               A001423
%K A001420 nonn,hard,nice
%O A001420 1,1
%A A001420 N. J. A. Sloane (njas(AT)research.att.com).
%E A001420 More terms from Brendan Owen (brendan_owen(AT)yahoo.com), Dec 15, 2001
%E A001420 a(28) from Joseph Myers (jsm(AT)polyomino.org.uk), Sep 24 2002
%E A001420 a(29)-a(31) from the Aleksandrowicz and Barequet paper (N. J. A. Sloane, 
               Jul 09 2009)