A263852 Number of 2-ascent sequences of length n with no consecutive repeated letters.

1, 1, 2, 6, 21, 87, 413, 2213, 13205, 86828, 623712, 4859307, 40810353, 367525528, 3532986232, 36107260781, 390938180027, 4470065574970, 53825174198772, 680796406765054, 9024180239004754, 125096535241364056, 1810074349321324370, 27289548352480937756

Offset

0,3

Links

Alois P. Heinz, Table of n, a(n) for n = 0..200

S. Kitaev, J. Remmel, p-Ascent Sequences, arXiv preprint arXiv:1503.00914 [math.CO], 2015.

Maple

b:= proc(n, i, t) option remember; `if`(n<1, 1, add(
      `if`(j=i, 0, b(n-1, j, t+`if`(j>i, 1, 0))), j=0..t+2))
    end:
a:= n-> b(n-1, 0$2):
seq(a(n), n=0..30);  # Alois P. Heinz, Nov 19 2015

Mathematica

b[n_, i_, t_] := b[n, i, t] = If[n<1, 1, Sum[If[j == i, 0, b[n-1, j, t + If[j>i, 1, 0]]], {j, 0, t+2}]]; a[n_] := b[n-1, 0, 0]; Table[a[n], {n, 0, 30}] (* Jean-François Alcover, Feb 17 2016, after Alois P. Heinz *)

Crossrefs

Column k=2 of A264909.

Sequence in context: A326335 A256180 A150227 * A189243 A033540 A177479

Adjacent sequences: A263849 A263850 A263851 * A263853 A263854 A263855

Keyword

nonn

Author

N. J. A. Sloane, Nov 18 2015

Extensions

a(10)-a(23) from Alois P. Heinz, Nov 19 2015

Status

approved