A229889 - OEIS

%I #10 Oct 04 2013 07:06:36

%S 1,1,1,1,1,1,1,1,1,1,9,45,165,495,1287,3003,6435,12870,207350,1782638,

%T 10852478,52422578,213586658,762311978,2445069626,7177825511,

%U 167072419775,2041472747275,17401832788275,116094500641665,645070724513865,3103383925397925

%N Number of 8 up, 8 down permutations of [n].

%H Alois P. Heinz, <a href="/A229889/b229889.txt">Table of n, a(n) for n = 0..200</a>

%e a(9) = 1: 123456789.

%p b:= proc(u, o, t) option remember; `if`(u+o=0, 1, add(`if`(t=8,

%p        b(o-j, u+j-1, 1), b(u+j-1, o-j, t+1)), j=1..o))

%p     end:

%p a:= n-> b(0, n, 0):

%p seq(a(n), n=0..35);

%Y Column k=8 of A229892.

%K nonn,eigen

%O 0,11

%A _Alois P. Heinz_, Oct 02 2013