

A092238


Number of ways to write the permutation n,n1,...,1 of 1,2,...,n as a product of n(n1)/2 transpositions, where each transposition of 1,2,...,n occurs exactly once.


0




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.


LINKS

Table of n, a(n) for n=0..6.


EXAMPLE

a(3)=2 because 321 = (1,2)(1,3)(2,3) = (2,3)(1,3)(1,2).


CROSSREFS

Cf. A005118.
Sequence in context: A085535 A060613 A139772 * A228252 A339305 A337651
Adjacent sequences: A092235 A092236 A092237 * A092239 A092240 A092241


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



