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
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