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A092238
Number of ways to write the permutation n,n-1,...,1 of 1,2,...,n as a product of n(n-1)/2 transpositions, where each transposition of 1,2,...,n occurs exactly once.
0
1, 1, 1, 2, 64, 59712, 3580519776
OFFSET
0,4
COMMENTS
If we impose the additional condition on the product t_1 t_2 ... of transpositions that the number of inversions increases by one each time we multiply by a t_i, then the number of ways is given by A005118.
EXAMPLE
a(3)=2 because 321 = (1,2)(1,3)(2,3) = (2,3)(1,3)(1,2).
CROSSREFS
Cf. A005118.
Sequence in context: A060613 A139772 A348214 * A228252 A339305 A337651
KEYWORD
more,nonn
AUTHOR
Richard Stanley, Feb 19 2004
EXTENSIONS
a(0)=1 prepended and a(6) added by Alois P. Heinz, Jul 12 2017
STATUS
approved