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Search: id:A005158
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| A005158 |
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Number of alternating sign n X n matrices invariant under a half-turn.
(Formerly M0902)
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+0
4
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| 1, 2, 3, 10, 25, 140, 588, 5544, 39204, 622908, 7422987
(list; graph; listen)
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OFFSET
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1,2
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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(2n) gives A059475.
Sequence in context: A059929 A123029 A103018 this_sequence A005225 A052929 A151415
Adjacent sequences: A005155 A005156 A005157 this_sequence A005159 A005160 A005161
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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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