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A005161
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Number of alternating sign 2n+1 X 2n+1 matrices symmetric with respect to both horizontal and vertical axes.
(Formerly M1700)
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1
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1, 1, 1, 2, 6, 33, 286, 4420, 109820, 4799134, 340879665, 42235307100, 8564558139000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,4
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REFERENCES
| 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
| I. Gessel and G. Xin, The generating function of ternary trees and continued fractions
P. Pyatov, Raise and Peel Models of fluctuating interfaces and combinatorics of Pascal's hexagon. [From Vladeta Jovovic (vladeta(AT)eunet.rs), Aug 15 2008]
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: A053042 A174432 A012874 * A062970 A088125 A064940
Adjacent sequences: A005158 A005159 A005160 * A005162 A005163 A005164
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KEYWORD
| nonn,nice,more
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| More terms (from the P. Pyatov paper) from Vladeta Jovovic (vladeta(AT)eunet.rs), Aug 15 2008
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