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A177528 Number of permutations of {1,...,n} avoiding adjacent step pattern up, down, up, down, down. 3
1, 1, 2, 6, 24, 120, 685, 4550, 34440, 292320, 2746800, 28402925, 320224500, 3909695400, 51396618000, 723952593000, 10876269801125, 173607227828250, 2934111079914750, 52343975053683000, 982945842995115000, 19381240178451775625, 400347201716808478750 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..454

FORMULA

a(n) ~ c * d^n * n!, where d = 0.93892752514028508419326638408810575968441290684141..., c = 1.4248368339815259677105814450156343177071690245... . - Vaclav Kotesovec, Jan 17 2015

MAPLE

b:= proc(u, o, t) option remember; `if`(t>5, 0, `if`(u+o+t<6, (u+o)!,

      add(b(u-j, o+j-1, [1, 3, 1, 5, 6][t]), j=1..u)+

      add(b(u+j-1, o-j, [2, 2, 4, 2, 4][t]), j=1..o)))

    end:

a:= n-> `if`(n=0, 1, add(b(j-1, n-j, 1), j=1..n)):

seq(a(n), n=0..25);  # Alois P. Heinz, Oct 21 2013

CROSSREFS

Columns k=20,26 of A242784.

Cf. A317639.

Sequence in context: A228393 A177526 A214611 * A177527 A068200 A189847

Adjacent sequences:  A177525 A177526 A177527 * A177529 A177530 A177531

KEYWORD

nonn

AUTHOR

R. H. Hardin, May 10 2010

EXTENSIONS

a(17)-a(22) from Alois P. Heinz, Oct 21 2013

STATUS

approved

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Last modified August 11 09:58 EDT 2020. Contains 336423 sequences. (Running on oeis4.)