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A030227 Number of n-celled polyominoes with bilateral symmetry. 2
1, 1, 2, 3, 6, 10, 20, 34, 70, 121, 250, 441, 912, 1630, 3375, 6092, 12624, 22961, 47616, 87136, 180811, 332549, 690398, 1275166, 2648422, 4909364, 10199792, 18966700, 39416488, 73497642, 152777230, 285569898, 593717419, 1112188817, 2312672439, 4340728280 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Polyominoes with n cells and at least one line of reflection symmetry. - Joshua Zucker, Mar 08 2008

LINKS

Table of n, a(n) for n=1..36.

FORMULA

a(n) = A000105(n) - A030228(n) = 2*A000105(n) - A000988(n). - Andrew Howroyd, Dec 04 2018

CROSSREFS

Cf. A000105, A000988, A006746, A030228.

Sequence in context: A135452 A077027 A030436 * A180272 A319436 A061551

Adjacent sequences:  A030224 A030225 A030226 * A030228 A030229 A030230

KEYWORD

nonn

AUTHOR

David W. Wilson

EXTENSIONS

a(23)-a(36) from Andrew Howroyd, Dec 04 2018

STATUS

approved

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Last modified January 19 23:25 EST 2019. Contains 319319 sequences. (Running on oeis4.)