A171579 Number of fixed polyominoes in equilibrium; a fixed polyomino is in equilibrium when its center of mass is vertically aligned with a cell with minimal coordinate.

0, 1, 1, 2, 5, 12, 27, 70, 192, 589, 1825, 5870, 18952, 62997, 211014, 718474, 2468741, 8578400

Offset: 1

Author

Mark Elduck (mark.elduck(AT)gmail.com), Dec 12 2009, Dec 20 2009, Dec 21 2009

Keywords

• hard
• more
• nonn

Examples

			For n=3, we have 2 fixed polyominoes in equilibrium: namely the vertical 3-omino and the horizontal 3-omino, thus a(3)=2.
		

Crossrefs

Cf. A001168