A229890 Number of 9 up, 9 down permutations of [n].

1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 10, 55, 220, 715, 2002, 5005, 11440, 24310, 48620, 880022, 8438222, 56936672, 303159572, 1354883102, 5281317614, 18427861739, 58640820239, 172577535989, 4529938877492, 62058701943644, 590100171030140, 4371834356234285

Offset

0,12

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=9,
       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=9 of A229892.

Sequence in context: A023035 A128936 A000582 * A243744 A145459 A290893

Adjacent sequences: A229887 A229888 A229889 * A229891 A229892 A229893

Keyword

nonn,eigen

Author

Alois P. Heinz, Oct 02 2013

Status

approved