A317289 - OEIS

%I #4 Jul 25 2018 16:38:37

%S 2404879675441,208031951035452,10539887638301128,438391470941407244,

%T 16755405367563104497,607314204208297961718,21247637795898419646167,

%U 729013114914519439841722,24775048055015061709737839,838857400014414535124226202,28428368151331776174951956983

%N Number of permutations of [n] with exactly nine increasing runs of even length.

%H Alois P. Heinz, <a href="/A317289/b317289.txt">Table of n, a(n) for n = 18..468</a>

%p b:= proc(u, o, t) option remember; series(`if`(u+o=0, x^t,

%p       add(b(u+j-1, o-j, irem(t+1, 2)), j=1..o)+

%p       add(b(u-j, o+j-1, 0)*x^t, j=1..u)), x, 10)

%p     end:

%p a:= n-> coeff(b(n, 0$2), x, 9):

%p seq(a(n), n=18..30);

%Y Column k=9 of A097592.

%K nonn

%O 18,1

%A _Alois P. Heinz_, Jul 25 2018