A351616 Number of free polyominoes with 2n squares, having 180-degree rotational symmetry about a vertex of a square, and no other symmetry.

0, 0, 1, 2, 12, 43, 174, 657, 2571, 9911, 38633, 150437, 588544, 2306204, 9061179, 35665587, 140648710, 555514177, 2197298561, 8702439446, 34506900216, 136972867380, 544237912916, 2164377093376, 8614630304437

Offset: 1

Author

John Mason, Feb 15 2022

Keywords

• nonn
• more

Comments

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

Examples

			a(3)=1 because of:
   OOO
  OOO
		

Crossrefs

Cf. A006747, A234008, A351615.

Extensions

a(17)-a(25) from John Mason, Feb 26 2023