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A030228 Number of chiral polyominoes with n cells. 6
1, 0, 0, 0, 2, 6, 25, 88, 335, 1215, 4534, 16823, 63159, 237679, 900341, 3423201, 13073163, 50095285, 192599091, 742576616, 2870584814, 11122879867, 43191525139, 168046317330, 654998425237, 2557224396342, 9999083912711, 39153000738695, 153511081627903 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

COMMENTS

A000105(n) + a(n) = A000988(n) because the number of free polyominoes plus the number of polyominoes lacking bilateral symmetry equals the number of one-sided polyominoes. - Graeme McRae, Jan 05 2006

LINKS

Andrew Howroyd, Table of n, a(n) for n = 0..45

D. H. Redelmeier, Counting polyominoes: yet another attack, Discrete Math., 36 (1981), 191-203.

FORMULA

a(n) = A000988(n) - A000105(n). - Graeme McRae, Jan 05 2006

a(n) = A006749(n) + A006747(n) + A144553(n). - Andrew Howroyd, Dec 04 2018

a(n) = A000105(n) - A030227(n) = (A000988(n) - A030227(n)) / 2. - Robert A. Russell, Feb 02 2019

EXAMPLE

For a(4)=2, the two chiral tetrominoes are XXX and XX .

                                           X        XX

MATHEMATICA

A000105 = Cases[Import["https://oeis.org/A000105/b000105.txt", "Table"], {_, _}][[All, 2]];

A000988 = Cases[Import["https://oeis.org/A000988/b000988.txt", "Table"], {_, _}][[All, 2]];

a[n_] := A000988[[n]] - A000105[[n + 1]];

Array[a, 45] (* Jean-Fran├žois Alcover, Sep 08 2019, after Graeme McRae *)

CROSSREFS

Cf. A000988 (oriented), A000105 (unoriented), A030227 (achiral).

Cf. A006747, A006749, A144553 (subcategories).

Sequence in context: A073545 A103063 A220191 * A066317 A027104 A019048

Adjacent sequences:  A030225 A030226 A030227 * A030229 A030230 A030231

KEYWORD

nonn

AUTHOR

David W. Wilson

EXTENSIONS

Terms a(23) and beyond from Andrew Howroyd, Dec 04 2018

Name edited by Robert A. Russell, Feb 03 2019

a(0)=1 added by N. J. A. Sloane, Jun 24 2020 at the suggestion of Fred Lunnon.

STATUS

approved

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Last modified April 13 01:36 EDT 2021. Contains 342934 sequences. (Running on oeis4.)