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A263854
Number of 4-ascent sequences of length n with no consecutive repeated letters.
2
1, 1, 4, 20, 110, 670, 4470, 32440, 254490, 2146525, 19374399, 186356108, 1903188611, 20569046543, 234562076984, 2814847291152, 35461339995304, 467952904377739, 6455368497736153, 92919917495585794, 1393239845937756837, 21726457354762648604
OFFSET
0,3
LINKS
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+4))
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 + 4}]]; 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=4 of A264909.
Sequence in context: A153295 A006770 A158827 * A026156 A025183 A014523
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Nov 18 2015
EXTENSIONS
a(10)-a(21) from Alois P. Heinz, Nov 19 2015
STATUS
approved