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A144553
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Number of chiral pairs of polyominoes with n cells that have precisely the symmetry group of order 4 generated by 90-degree rotations.
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29
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0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 3, 2, 0, 0, 12, 7, 0, 0, 44, 25, 0, 0, 165, 90, 0, 0, 603, 319, 0, 0, 2235, 1136, 0, 0, 8283, 4088, 0, 0, 30936, 14868, 0, 0, 116111, 54526, 0, 0, 438465, 201527, 0, 0, 1663720, 750169, 0, 0, 6342211, 2809931, 0, 0, 24273767
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OFFSET
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1,12
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COMMENTS
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The values for n>28 were produced by a set of programs, the most difficult of which is attached. There is no guarantee that the values are correct, although presumably Shirakawa has calculated them through a(45). The attached program can be altered to count only achiral polyominoes, and those results match those of A142886, which uses a very different method. The difficulties lie in determining each inner loop (A324408 and A324409) and in determining connections within the inner loop (bad_connection subroutine). The last bug I found in the program affected only polyominoes with 72 or more cells. - Robert A. Russell, May 23 2020
These are polyominoes of the regular tiling with Schläfli symbol {4,4}. In late August, 2021, John Mason informed me that there were errors for a(44) and higher. My error in a(44) was a copying error, but later entries were wrong because of my programming errors. After making corrections (see attached C++ program), our values now match. John uses a unique calculation of his own devising. Since it is quite different from Redelmeier's inner rings, the match gives us some confidence in the current values. - Robert A. Russell, Nov 01 2021
Polyominoes with precisely 90-degree symmetry centered about square centers and vertices are enumerated by A351142 and A234007 respectively. - John Mason, Feb 17 2022
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LINKS
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Robert A. Russell, Table of n, a(n) for n = 1..95
Tomás Oliveira e Silva, Enumeration of polyominoes
D. H. Redelmeier, Counting polyominoes: yet another attack, Discrete Math., 36 (1981), 191-203.
D. H. Redelmeier, Table 3 of Counting polyominoes...
Robert A. Russell, C++ Program
Toshihiro Shirakawa, Enumeration of Polyominoes considering the symmetry, April 2012, pp. 3-4.
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FORMULA
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a(n) = A030228(n) - A006747(n) - A006749(n). - Jean-François Alcover, Sep 09 2019, after Andrew Howroyd in A030228.
a(n) = (A348848(n/4)+A348849(n)-A142886(n)) / 2, where the first two are F90 and C90 of the Shirakawa link. - Robert A. Russell, Nov 01 2021
a(n) = A351142(n) + A234007(n/4) if n is a multiple of 4, otherwise a(n) = A351142(n). - John Mason, Feb 17 2022
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EXAMPLE
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For a(8)=1, the polyomino is a central 2 X 2 square with one cell attached to each edge of that square. - Robert A. Russell, Nov 01 2021
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MATHEMATICA
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A006747 = Cases[Import["https://oeis.org/A006747/b006747.txt",
"Table"], {_, _}][[All, 2]];
A006749 = Cases[Import["https://oeis.org/A006749/b006749.txt",
"Table"], {_, _}][[All, 2]];
A030228 = Cases[Import["https://oeis.org/A030228/b030228.txt",
"Table"], {_, _}][[All, 2]];
a[n_] := A030228[[n]] - A006747[[n]] - A006749[[n]];
Array[a, 28] (* Jean-François Alcover, Sep 09 2019 *)
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CROSSREFS
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Sequences classifying polyominoes by symmetry group: A000105, A006746, A006747, A006748, A006749, A056877, A056878, A142886, A144553, A144554, A351142, A234007.
Cf. A324408, A324409 (inner rings).
Cf. A348848 (C90), A348849 (F90).
Sequence in context: A246159 A059033 A133209 * A187130 A187145 A285700
Adjacent sequences: A144550 A144551 A144552 * A144554 A144555 A144556
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KEYWORD
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nonn,more
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AUTHOR
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N. J. A. Sloane, Jan 01 2009
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EXTENSIONS
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a(28) added by Andrew Howroyd, Dec 04 2018
a(29)-a(91) added by Robert A. Russell, May 23 2020
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STATUS
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approved
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