OFFSET
1,2
COMMENTS
Sequence suggested by Leroy Quet on the SeqFan mailing list.
EXAMPLE
a(4)=9, since the 9 permutations (1,2,3,4), (1,4,3,2), (2,1,3,4), (2,1,4,3), (2,3,4,1), (4,1,2,3), (3,2,1,4), (3,4,1,2), (4,3,2,1) satisfy the property.
CROSSREFS
KEYWORD
nonn
AUTHOR
Giovanni Resta, Mar 28 2006
STATUS
approved