A229890 - OEIS

%I #9 Oct 04 2013 07:41:14

%S 1,1,1,1,1,1,1,1,1,1,1,10,55,220,715,2002,5005,11440,24310,48620,

%T 880022,8438222,56936672,303159572,1354883102,5281317614,18427861739,

%U 58640820239,172577535989,4529938877492,62058701943644,590100171030140,4371834356234285

%N Number of 9 up, 9 down permutations of [n].

%H Alois P. Heinz, <a href="/A229890/b229890.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=9,

%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=9 of A229892.

%K nonn,eigen

%O 0,12

%A _Alois P. Heinz_, Oct 02 2013