A317284 Number of permutations of [n] with exactly four increasing runs of even length.

1385, 31493, 460929, 6632158, 99592344, 1489928080, 22566676855, 354404597721, 5758011600442, 96477356811365, 1673128285327455, 30065282456829860, 558998263719383722, 10749166166477149832, 213755085162112473899, 4392507334767609209209, 93197430506980061714657

Offset: 8

Author

Alois P. Heinz, Jul 25 2018

Keywords

• nonn

Links

• Alois P. Heinz, Table of n, a(n) for n = 8..471

Crossrefs

Column k=4 of A097592.

Programs

Maple

b:= proc(u, o, t) option remember; series(`if`(u+o=0, x^t,
      add(b(u+j-1, o-j, irem(t+1, 2)), j=1..o)+
      add(b(u-j, o+j-1, 0)*x^t, j=1..u)), x, 5)
    end:
a:= n-> coeff(b(n, 0$2), x, 4):
seq(a(n), n=8..30);