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Search: id:A005162
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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
1
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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; listen)
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OFFSET
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1,2
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REFERENCES
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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.
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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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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Sequence in context: A006882 A080498 A133983 this_sequence A129108 A100321 A121133
Adjacent sequences: A005159 A005160 A005161 this_sequence A005163 A005164 A005165
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KEYWORD
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nonn,nice,more
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AUTHOR
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njas and Simon Plouffe (plouffe(AT)math.uqam.ca)
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