A317283 Number of permutations of [n] with exactly three increasing runs of even length.

61, 906, 8965, 94398, 1088575, 12625694, 150890533, 1914036434, 25485825638, 353702731940, 5141233861254, 78259458749608, 1243051438276365, 20579839942072222, 354951501710697119, 6367683567830126402, 118640486378324764141, 2293339890430027143606

Offset: 6

Author

Alois P. Heinz, Jul 25 2018

Keywords

• nonn

Links

• Alois P. Heinz, Table of n, a(n) for n = 6..472

Crossrefs

Column k=3 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, 4)
    end:
a:= n-> coeff(b(n, 0$2), x, 3):
seq(a(n), n=6..30);