A180889 Number of permutations of 1..n with no element greater than or equal to the sum of its neighbors.

1, 0, 0, 4, 12, 40, 204, 1500, 10712, 84044, 722068, 6961952, 71944504, 805668712, 9597694448, 122786050180, 1662100961328

Offset

1,4

Links

Table of n, a(n) for n=1..17.

Example

All solutions for n=5
(1 2 3 5 4) (1 2 4 5 3) (1 2 5 4 3) (1 3 4 5 2)
(1 3 5 4 2) (1 4 5 3 2) (2 3 5 4 1) (2 4 5 3 1)
(2 5 4 3 1) (3 4 5 2 1) (3 5 4 2 1) (4 5 3 2 1)

Crossrefs

Sequence in context: A149340 A387603 A246317 * A002996 A076867 A308369

Adjacent sequences: A180886 A180887 A180888 * A180890 A180891 A180892

Keyword

nonn

Author

R. H. Hardin, Sep 23 2010

Status

approved