A351615 Number of free polyominoes with n squares, having 180-degree rotational symmetry about the center of a square, and no other symmetry.

0, 0, 0, 0, 1, 0, 4, 0, 19, 1, 73, 4, 283, 25, 1090, 106, 4183, 463, 16105, 1892, 62170, 7752, 240907, 31212, 936447, 125609, 3651618, 503165, 14277519, 2014826, 55961118, 8058790, 219813564, 32231897, 865091976, 128897247, 3410498446, 515554767, 13466262587, 2062445063, 53245595410, 8252868076, 210800433323

Offset: 1

Author

John Mason, Feb 15 2022

Keywords

• nonn

Comments

The sequence enumerates a subset of the polyominoes enumerated by A006747.

Examples

			a(5)=1 because of:
   OO
   O
  OO
		

Links

• John Mason, Table of n, a(n) for n = 1..50

Crossrefs

Cf. A006747, A234008, A351616.

Extensions

More terms from John Mason, Apr 15 2023