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A006747 Number of rotationally symmetric polyominoes with n cells.
(Formerly M3741)
20

%I M3741

%S 0,0,0,1,1,5,4,18,19,73,73,278,283,1076,1090,4125,4183,15939,16105,

%T 61628,62170,239388,240907,932230,936447,3641945,3651618,14262540

%N Number of rotationally symmetric polyominoes with n cells.

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

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

%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

%H Tomás Oliveira e Silva, <a href="http://sweet.ua.pt/tos/animals.html">Enumeration of polyominoes</a>

%H D. H. Redelmeier, <a href="/A056877/a056877.png">Table 3</a> of Counting polyominoes...

%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 1,6

%A _N. J. A. Sloane_

%E Extended to n=28 by Tomás Oliveira e Silva

%E a(1)-a(3) prepended by _Andrew Howroyd_, Dec 04 2018

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Last modified February 19 10:34 EST 2019. Contains 320310 sequences. (Running on oeis4.)