%I A056877
%S A056877 0,1,1,1,1,2,3,4,4,8,10,15,17,30,35,60,64,117,128,236,241,459,476,
%T A056877 937,912,1813,1789,3706
%N A056877 Number of polyominoes with n cells, symmetric about axis 2.
%C A056877 This sequence counts polyominoes with exactly the symmetry group D_4 
               generated by horizontal and vertical reflections.
%D A056877 D. H. Redelmeier, Counting polyominoes: yet another attack, Discrete 
               Math., 36 (1981), 191-203.
%H A056877 Tomas Oliveira e Silva, <a href="http://www.ieeta.pt/~tos/animals.html">
               Enumeration of polyominoes</a>
%H A056877 D. H. Redelmeier, <a href="a056877.png">Table 3</a> of Counting polyominoes...
%Y A056877 Cf. A000105, A001168, A006746, A056877, A006748, A056878, A006747, A006749.
%Y A056877 Sequences classifying polyominoes by symmetry group: A000105, A006746, 
               A006747, A006748, A006749, A056877, A056878, A142886, A144553, A144554.
%Y A056877 Sequence in context: A028298 A047966 A097093 this_sequence A118263 A102539 
               A118022
%Y A056877 Adjacent sequences: A056874 A056875 A056876 this_sequence A056878 A056879 
               A056880
%K A056877 nonn
%O A056877 1,6
%A A056877 N. J. A. Sloane (njas(AT)research.att.com), Sep 03 2000