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A057724 Number of "polyares" of order n (turning over allowed). 2
1, 3, 9, 42, 180, 889, 4392, 224332 (list; graph; refs; listen; history; internal format)
OFFSET

1,2

COMMENTS

An n-are is a shape formed from an n-celled polyominoe by removing half of each square cell in such a way that at least half of the original join between cells is retained.

REFERENCES

Enumeration attributed by Andrew Clarke to Brendan Owen.

LINKS

Andrew Clarke, Polyares

Picture from Andrew Clarke's page showing the 9 polyares of order 3 when turning over is allowed.

Eric Weisstein's World of Mathematics, Polyare

CROSSREFS

Cf. A057725, A000105.

Sequence in context: A139150 A113271 A183306 * A129879 A001427 A020128

Adjacent sequences:  A057721 A057722 A057723 * A057725 A057726 A057727

KEYWORD

nonn,nice

AUTHOR

N. J. A. Sloane (njas(AT)research.att.com), Oct 29 2000

EXTENSIONS

Link updated by William Rex Marshall (w.r.marshall(AT)actrix.co.nz), Dec 16 2009

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Last modified February 15 13:43 EST 2012. Contains 205805 sequences.