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A006747 Number of rotationally symmetric polyominoes with n cells.
(Formerly M3741)
13
1, 1, 5, 4, 18, 19, 73, 73, 278, 283, 1076, 1090, 4125, 4183, 15939, 16105, 61628, 62170, 239388, 240907, 932230, 936447, 3641945, 3651618, 14262540 (list; graph; refs; listen; history; text; internal format)
OFFSET

4,3

COMMENTS

This sequence counts polyominoes with exactly the symmetry group C_2 generated by a 180 degree rotation.

REFERENCES

D. H. Redelmeier, Counting polyominoes: yet another attack, Discrete Math., 36 (1981), 191-203.

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=4..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: A190728 A100791 A056883 * A184297 A108412 A205008

Adjacent sequences:  A006744 A006745 A006746 * A006748 A006749 A006750

KEYWORD

nonn

AUTHOR

N. J. A. Sloane.

EXTENSIONS

Extended to n=28 by Tomas Oliveira e Silva.

STATUS

approved

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Last modified September 1 17:37 EDT 2014. Contains 246309 sequences.