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A177539 Number of permutations of {1,...,n} avoiding adjacent step pattern up, down, down, up, down, up. 2
1, 1, 2, 6, 24, 120, 720, 4859, 37424, 323784, 3107520, 32749200, 376929246, 4698101279, 63058148792, 906829731450, 13911580276800, 226738605155619, 3912973221007668, 71280397766349665, 1366816300552776920, 27519285653572655340, 580456044040809459821 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,3
LINKS
FORMULA
a(n) ~ c * d^n * n!, where d = 0.958757960478580745672487123002941621817..., c = 1.30438280919882137519668832091857761... . - Vaclav Kotesovec, Jan 17 2015
MAPLE
b:= proc(u, o, t) option remember; `if`(t>6, 0, `if`(u+o+t<7, (u+o)!,
add(b(u-j, o+j-1, [1, 3, 4, 1, 6, 4][t]), j=1..u)+
add(b(u+j-1, o-j, [2, 2, 2, 5, 2, 7][t]), j=1..o)))
end:
a:= n-> b(n, 0, 1):
seq(a(n), n=0..25); # Alois P. Heinz, Oct 24 2013
MATHEMATICA
b[u_, o_, t_] := b[u, o, t] = If[t > 6, 0, If[u + o + t < 7, (u + o)!,
Sum[b[u - j, o + j - 1, {1, 3, 4, 1, 6, 4}[[t]]], {j, 1, u}] +
Sum[b[u + j - 1, o - j, {2, 2, 2, 5, 2, 7}[[t]]], {j, 1, o}]]];
a[n_] := b[n, 0, 1];
Table[a[n], {n, 0, 25}] (* Jean-François Alcover, Apr 19 2022, after Alois P. Heinz *)
CROSSREFS
Columns k=37,41 of A242784.
Sequence in context: A147739 A147738 A147737 * A177546 A177544 A177540
KEYWORD
nonn
AUTHOR
R. H. Hardin, May 10 2010
EXTENSIONS
a(17)-a(22) from Alois P. Heinz, Oct 24 2013
STATUS
approved

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Last modified March 29 05:48 EDT 2024. Contains 371265 sequences. (Running on oeis4.)