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A005160 Number of alternating sign n X n matrices invariant under a quarter turn.
(Formerly M0396)
4
1, 0, 1, 2, 3, 0, 12, 40, 100, 0, 1225, 6860, 28812, 0, 1037232, 9779616 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,4
COMMENTS
Robbins incorrectly gives a(12) = 6460.
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.
LINKS
G. Kuperberg, Symmetry classes of alternating-sign matrices under one roof, arXiv:math/0008184 [math.CO], 2000-2001.
D. P. Robbins, Symmetry classes of alternating sign matrices, arXiv:math/0008045 [math.CO], 2000.
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. Preprint. [Annotated scanned copy]
FORMULA
Robbins gives a simple (conjectured) formula.
CROSSREFS
a(4n) gives A059476.
Sequence in context: A265514 A219341 A059740 * A085042 A096542 A009206
KEYWORD
nonn,nice,more
AUTHOR
STATUS
approved

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Last modified March 19 02:55 EDT 2024. Contains 370952 sequences. (Running on oeis4.)