OFFSET

1,2

COMMENTS

Sequence suggested by Leroy Quet on the SeqFan mailing list.

EXAMPLE

a(4)=8, since the 8 permutations (1,2,3,4), (1,4,3,2), (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