|
| |
|
|
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; 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
| 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: A012404 A002099 A059740 * A085042 A096542 A009206
Adjacent sequences: A005157 A005158 A005159 * A005161 A005162 A005163
|
|
|
KEYWORD
| nonn,nice,more
|
|
|
AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
|
|
|
EXTENSIONS
| Robbins incorrectly gives a(12) = 6460.
|
| |
|
|
