

A006746


Number of axially symmetric polyominoes with n cells.
(Formerly M1573)


21



0, 0, 0, 1, 2, 6, 9, 23, 38, 90, 147, 341, 564, 1294, 2148, 4896, 8195, 18612, 31349, 70983, 120357, 271921, 463712, 1045559, 1792582, 4034832, 6950579, 15619507
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,5


COMMENTS

Number of polyominoes with n cells and exactly one line of reflection symmetry, where that one line is parallel to the grid.  Joshua Zucker, Mar 08 2008


REFERENCES

D. H. Redelmeier, Counting polyominoes: yet another attack, Discrete Math., 36 (1981), 191203.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

Table of n, a(n) for n=1..28.
Tomás Oliveira e Silva, Enumeration of polyominoes
D. H. Redelmeier, Table 3 of Counting polyominoes...


CROSSREFS

Cf. A000105, A001168, A006746, A056877, A006748, A056878, A006747, A006749, A030227.
Sequences classifying polyominoes by symmetry group: A000105, A006746, A006747, A006748, A006749, A056877, A056878, A142886, A144553, A144554.
Sequence in context: A127931 A077237 A056879 * A205875 A243558 A244427
Adjacent sequences: A006743 A006744 A006745 * A006747 A006748 A006749


KEYWORD

nonn


AUTHOR

N. J. A. Sloane.


EXTENSIONS

Extended to n=28 by Tomás Oliveira e Silva.


STATUS

approved



