%I
%S 0,0,0,0,0,0,1,1,0,1,2,3,3,5,6,14,9,20,20,56,32,80,64,224,114,315,217,
%T 863,397,1234,751,3331,1400,4816,2632,12815,4973,18792,9349,49400,
%U 17810,73338,33557,190643,64309,286368,121511,737532,233891,1119215,443271,2859154
%N Number of polyominoes with n cells, symmetric about diagonal 2.
%H Robert A. Russell, <a href="/A056878/b056878.txt">Table of n, a(n) for n = 1..87</a>
%H Tomás Oliveira e Silva, <a href="http://sweet.ua.pt/tos/animals.html">Enumeration of polyominoes</a>
%H D. H. Redelmeier, <a href="http://dx.doi.org/10.1016/0012365X(81)902375">Counting polyominoes: yet another attack</a>, Discrete Math., 36 (1981), 191203.
%H D. H. Redelmeier, <a href="/A056877/a056877.png">Table 3</a> of Counting polyominoes...
%e For a(7)=1, the heptomino with exactly fourfold symmetry and axes of symmetry parallel to the diagonals of the cells is composed of two 2 X 2 squares with one cell in common. For a(8)=1, the octomino is composed of a 2 X 2 square and the four cells adjacent to two nonadjacent cells of that square.
%Y Cf. A000105, A001168, A006746, A056877, A006748, A056878, A006747, A006749.
%Y Sequences classifying polyominoes by symmetry group: A000105, A006746, A006747, A006748, A006749, A056877, A056878, A142886, A144553, A144554.
%K nonn
%O 1,11
%A _N. J. A. Sloane_, Sep 03 2000
%E More terms from _Robert A. Russell_, Jan 18 2019
