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Search: id:A005160
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| A005160 |
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Number of alternating sign n X n matrices invariant under a quarter turn.
(Formerly M0396)
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+0
4
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| 1, 0, 1, 2, 3, 0, 12, 40, 100, 0, 1225, 6860, 28812, 0, 1037232, 9779616
(list; graph; listen)
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OFFSET
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1,4
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
R. P. Stanley, A baker's dozen of conjectures concerning plane partitions, pp. 285-293 of "Combinatoire Enumerative (Montreal 1985)", Lect. Notes Math. 1234, 1986.
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LINKS
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G. Kuperberg, Symmetry classes of alternating-sign matrices under one roof, arXiv math.CO/0008184
D. P. Robbins, Symmetry classes of alternating sign matrices, arXiv:math.CO/0008045
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FORMULA
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Robbins gives a simple (conjectured) formula.
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CROSSREFS
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a(4n) gives A059476.
Sequence in context: A012404 A002099 A059740 this_sequence A085042 A096542 A009206
Adjacent sequences: A005157 A005158 A005159 this_sequence A005161 A005162 A005163
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KEYWORD
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nonn,nice,more
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
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Robbins incorrectly gives a(12) = 6460.
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