A057424 Diagonally symmetric (about diagonal 2) 2n-celled polyominoes with 1 hole.

1, 1, 5, 7, 21, 30, 88, 116, 336, 439, 1271, 1639, 4713, 6088, 17452

Offset: 6

Author

N. J. A. Sloane, Sep 05 2000

Keywords

• nonn
• more

Comments

The sequence refers to polyominoes with one hole and both diagonal symmetries but no other. - John Mason, Jan 16 2023

Links

• Tomás Oliveira e Silva, Enumeration of polyominoes

Crossrefs

Cf. A056882.

Extensions

a(15)-a(20) from John Mason, Jan 16 2023