A229889 Number of 8 up, 8 down permutations of [n].

1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 9, 45, 165, 495, 1287, 3003, 6435, 12870, 207350, 1782638, 10852478, 52422578, 213586658, 762311978, 2445069626, 7177825511, 167072419775, 2041472747275, 17401832788275, 116094500641665, 645070724513865, 3103383925397925

Offset

0,11

Links

Alois P. Heinz, Table of n, a(n) for n = 0..200

Example

a(9) = 1: 123456789.

Maple

b:= proc(u, o, t) option remember; `if`(u+o=0, 1, add(`if`(t=8,
       b(o-j, u+j-1, 1), b(u+j-1, o-j, t+1)), j=1..o))
    end:
a:= n-> b(0, n, 0):
seq(a(n), n=0..35);

Crossrefs

Column k=8 of A229892.

Sequence in context: A023034 A000581 A306939 * A243743 A145458 A145137

Adjacent sequences: A229886 A229887 A229888 * A229890 A229891 A229892

Keyword

nonn,eigen

Author

Alois P. Heinz, Oct 02 2013

Status

approved