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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
0, 1, 1, 2, 5, 12, 27, 70, 192, 589, 1825, 5870, 18952, 62997, 211014, 718474, 2468741, 8578400
OFFSET
1,4
EXAMPLE
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
Sequence in context: A026710 A291248 A316706 * A228638 A202604 A118898
KEYWORD
hard,more,nonn
AUTHOR
Mark Elduck (mark.elduck(AT)gmail.com), Dec 12 2009, Dec 20 2009, Dec 21 2009
STATUS
approved