|
| |
|
|
A056878
|
|
Number of polyominoes with n cells, symmetric about diagonal 2.
|
|
20
|
|
|
|
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, 863, 397, 1234, 751, 3331, 1400, 4816, 2632, 12815, 4973, 18792, 9349, 49400, 17810, 73338, 33557, 190643, 64309, 286368, 121511, 737532, 233891, 1119215, 443271, 2859154
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,11
|
|
|
LINKS
|
Robert A. Russell, Table of n, a(n) for n = 1..87
Tomás Oliveira e Silva, Enumeration of polyominoes
D. H. Redelmeier, Counting polyominoes: yet another attack, Discrete Math., 36 (1981), 191-203.
D. H. Redelmeier, Table 3 of Counting polyominoes...
|
|
|
EXAMPLE
|
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.
|
|
|
CROSSREFS
|
Cf. A000105, A001168, A006746, A056877, A006748, A056878, A006747, A006749.
Sequences classifying polyominoes by symmetry group: A000105, A006746, A006747, A006748, A006749, A056877, A056878, A142886, A144553, A144554.
Sequence in context: A121400 A238003 A218932 * A270520 A092557 A333295
Adjacent sequences: A056875 A056876 A056877 * A056879 A056880 A056881
|
|
|
KEYWORD
|
nonn
|
|
|
AUTHOR
|
N. J. A. Sloane, Sep 03 2000
|
|
|
EXTENSIONS
|
More terms from Robert A. Russell, Jan 18 2019
|
|
|
STATUS
|
approved
|
| |
|
|
