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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

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

Table of n, a(n) for n=1..16.

G. Kuperberg, Symmetry classes of alternating-sign matrices under one roof, arXiv math.CO/0008184

D. P. Robbins, Symmetry classes of alternating sign matrices, arXiv:math.CO/0008045

FORMULA

Robbins gives a simple (conjectured) formula.

CROSSREFS

a(4n) gives A059476.

Sequence in context: A002099 A219341 A059740 * A085042 A096542 A009206

Adjacent sequences:  A005157 A005158 A005159 * A005161 A005162 A005163

KEYWORD

nonn,nice,more

AUTHOR

N. J. A. Sloane.

EXTENSIONS

Robbins incorrectly gives a(12) = 6460.

STATUS

approved

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Last modified April 21 12:08 EDT 2014. Contains 240824 sequences.