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A056880
Number of n-celled polyominoes without holes, symmetric about axis 2.
3
0, 1, 1, 1, 1, 2, 3, 4, 4, 6, 10, 11, 16, 18, 33, 34, 56, 56, 110, 106, 193, 177, 372, 335, 662, 571, 1269, 1084, 2282, 1875, 4365, 3568, 7914, 6257, 15141, 11935, 27615, 21170, 52911, 40486, 96980, 72490, 186144, 138981, 342638, 250814, 658884, 482029, 1217327, 875697, 2345272, 1686803
OFFSET
1,6
COMMENTS
In other words, free polyominoes, without holes, with both vertical and horizontal symmetries but no other. - John Mason, Oct 10 2022
CROSSREFS
Cf. A000104, A056877 (with holes allowed).
Sequence in context: A296116 A017832 A347713 * A053273 A347700 A049988
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Sep 03 2000
EXTENSIONS
a(29)-a(52) from John Mason, Oct 10 2022
STATUS
approved