A351190 Number of polyominoes of n cells with both horizontal and vertical symmetries, for which the 180-degree rotational symmetry has an axis that coincides with the center of a square, but without 90-degree rotational symmetry.

0, 0, 1, 0, 1, 0, 3, 0, 4, 1, 10, 3, 17, 6, 35, 15, 64, 31, 128, 74, 241, 145, 476, 332, 912, 649, 1789, 1446, 3456, 2821, 6779, 6164, 13161, 12049, 25839, 25981, 50348, 50844, 98957, 108514, 193375, 212766, 380522, 450568, 745248, 884843, 1468202, 1862065, 2880780, 3662652, 5681501, 7668922

Offset: 1

Author

John Mason, Feb 04 2022

Keywords

• nonn

Comments

This sequence enumerates a subset of the polyominoes enumerated by A056877.

Examples

			a(3)=1 because of the straight tromino.
		

Crossrefs

Cf. A000105, A056877.

Extensions

More terms from John Mason, Mar 15 2023