A056880 Number of n-celled polyominoes without holes, symmetric about axis 2.

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

Author

N. J. A. Sloane, Sep 03 2000

Keywords

• nonn

Comments

In other words, free polyominoes, without holes, with both vertical and horizontal symmetries but no other. - John Mason, Oct 10 2022

Links

• Tomás Oliveira e Silva, Enumeration of polyominoes

Crossrefs

Cf. A000104, A056877 (with holes allowed).

Extensions

a(29)-a(52) from John Mason, Oct 10 2022