A317282 Number of permutations of [n] with exactly two increasing runs of even length.

5, 43, 258, 1853, 15634, 133697, 1207256, 11974457, 126980013, 1421291622, 16925790480, 213992804118, 2851968574855, 39996895523591, 589713707701692, 9114791365659163, 147335664946835342, 2486973983349027871, 43763134470537718258, 801419373432471123541

Offset

4,1

Links

Alois P. Heinz, Table of n, a(n) for n = 4..472

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

Crossrefs

Column k=2 of A097592.

Sequence in context: A173554 A126963 A221874 * A182191 A038140 A178826

Adjacent sequences: A317279 A317280 A317281 * A317283 A317284 A317285

Keyword

nonn

Author

Alois P. Heinz, Jul 25 2018

Status

approved