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A217595
Number of free n-celled polyominoes without holes and odd side lengths.
1
1, 0, 1, 1, 2, 4, 7, 12, 35, 55, 144, 335, 710, 1791, 4195
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.
EXAMPLE
For n=5 the a(5)=2 pentominoes are 'I' and 'X'.
CROSSREFS
Sequence in context: A309729 A027945 A079800 * A280028 A094271 A194422
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 Aurélien Ooms, Nov 14-19 2019
STATUS
approved