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A005164
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Number of alternating sign 2n+1 X 2n+1 matrices invariant under all symmetries of the square.
(Formerly M1271)
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3
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1, 1, 1, 2, 4, 13, 46, 248, 1516, 13654, 142873, 2156888, 38456356, 974936056
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,4
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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
| Cf. A005130, A057628.
Sequence in context: A007858 A153930 A184177 * A058134 A069730 A072605
Adjacent sequences: A005161 A005162 A005163 * A005165 A005166 A005167
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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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