A217595 Number of free n-celled polyominoes without holes and odd side lengths.

1, 0, 1, 1, 2, 4, 7, 12, 35, 55, 144, 335, 710, 1791, 4195

Offset: 1

Author

Thomas Dybdahl Ahle, May 28 2013

Keywords

• nonn
• hard
• more

Comments

If you checkerboard color the vertices of the square lattice, a(n) is the number of orthogonal polygons of area n, which alternates between white and black vertices.

Examples

			For n=5 the a(5)=2 pentominoes are 'I' and 'X'.
		

Links

• Giovanni Resta, Illustration of a(10) = 55.

Extensions

a(10) from Giovanni Resta, Jun 06 2013

a(11)-a(12) from Thomas Dybdahl Ahle, Nov 13 2019

a(13)-a(15) from Aurélien Ooms, Nov 14-19 2019