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A201973
Numbers of configurations of n-1 linear orderings on {1..n} up to equivalence.
0
1, 2, 21, 5097, 71965235
OFFSET
2,2
COMMENTS
A configuration is a set of n-1 linear orderings <_1, .., <_(n-1) on {1..n}.
A reversion of an ordering is the ordering obtained by reversing every inequality in this ordering.
Two configurations are equivalent if they are equal up to:
- a permutation of <_1, .., <_(n-1)
- a permutation of {1..n}
- some reversions of orderings
REFERENCES
E. Gioan, K. Sol and G. Subsol, Orientations of Simplices Determined by Orderings on the Coordinates of their Vertices, In Proc. of 23rd CCCG, 187-192, 2011.
EXAMPLE
For n=3, the a(3)=2 configurations up to equivalence are: (1 <_1 2 <_1 3; 1 <_2 2 <_2 3) and (1 <_1 2 <_1 3; 1 <_2 3 <_2 2).
CROSSREFS
Sequence in context: A276654 A114846 A195165 * A278737 A162393 A328993
KEYWORD
nonn
AUTHOR
Kevin SOl, Dec 07 2011
EXTENSIONS
71965235 added by Kevin SOl, May 30 2012
STATUS
approved