

A217595


Number of free ncelled polyominoes without holes and odd side lengths.


1



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

1,5


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.


LINKS

Table of n, a(n) for n=1..15.
Giovanni Resta, Illustration of a(10) = 55.


EXAMPLE

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


CROSSREFS

Sequence in context: A309729 A027945 A079800 * A280028 A094271 A194422
Adjacent sequences: A217592 A217593 A217594 * A217596 A217597 A217598


KEYWORD

nonn,hard,more


AUTHOR

Thomas Dybdahl Ahle, May 28 2013


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 AurĂ©lien Ooms, Nov 1419 2019


STATUS

approved



