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A005162
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Number of alternating sign n X n matrices symmetric with respect to both diagonals.
(Formerly M0877)
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0
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1, 2, 3, 8, 15, 52, 126, 568, 1782, 10436, 42471, 323144, 1706562, 16866856, 115640460, 1484714416, 13216815036, 220426128584, 2548124192970
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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REFERENCES
| M. Bousquet-Melou and L. Habsieger, Sur les matrices a signes alternants, S\'{e}ries Formelles et Combinatoire Alg\'{e}brique, 4th colloquium, 15-19 Juin 1992, Montr\'{e}al, Universit\'{e} du Qu\'{e}bec \`{a} Montr\'{e}al, pp. 19-32.
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
| D. P. Robbins, Symmetry classes of alternating sign matrices, arXiv:math.CO/0008045
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FORMULA
| Robbins gives a simple (conjectured) formula.
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CROSSREFS
| Sequence in context: A080498 A148013 A133983 * A129108 A160622 A153699
Adjacent sequences: A005159 A005160 A005161 * A005163 A005164 A005165
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KEYWORD
| nonn,nice,more
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com) and Simon Plouffe (simon.plouffe(AT)gmail.com)
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