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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

LINKS

Table of n, a(n) for n=1..18.

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

Cf. A001168

Sequence in context: A026710 A291248 A316706 * A228638 A202604 A118898

Adjacent sequences:  A171576 A171577 A171578 * A171580 A171581 A171582

KEYWORD

hard,more,nonn

AUTHOR

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

STATUS

approved

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Last modified January 21 05:23 EST 2020. Contains 331104 sequences. (Running on oeis4.)