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%I #17 May 30 2012 12:17:04
%S 1,2,21,5097,71965235
%N Numbers of configurations of n-1 linear orderings on {1..n} up to equivalence.
%C A configuration is a set of n-1 linear orderings <_1, .., <_(n-1) on {1..n}.
%C A reversion of an ordering is the ordering obtained by reversing every inequality in this ordering.
%C Two configurations are equivalent if they are equal up to:
%C - a permutation of <_1, .., <_(n-1)
%C - a permutation of {1..n}
%C - some reversions of orderings
%D 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.
%e 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).
%K nonn
%O 2,2
%A _Kevin SOl_, Dec 07 2011
%E 71965235 added by _Kevin SOl_, May 30 2012
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