

A056877


Number of polyominoes with n cells, symmetric about axis 2.


13



0, 1, 1, 1, 1, 2, 3, 4, 4, 8, 10, 15, 17, 30, 35, 60, 64, 117, 128, 236, 241, 459, 476, 937, 912, 1813, 1789, 3706
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OFFSET

1,6


COMMENTS

This sequence counts polyominoes with exactly the symmetry group D_4 generated by horizontal and vertical reflections.


REFERENCES

D. H. Redelmeier, Counting polyominoes: yet another attack, Discrete Math., 36 (1981), 191203.


LINKS

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


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: A224038 A241037 A097093 * A228461 A244940 A244832
Adjacent sequences: A056874 A056875 A056876 * A056878 A056879 A056880


KEYWORD

nonn


AUTHOR

N. J. A. Sloane, Sep 03 2000


STATUS

approved



