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A177520 Number of permutations of 1..n avoiding adjacent step pattern up, down, up, down. 3
1, 1, 2, 6, 24, 104, 528, 3296, 23168, 179712, 1573632, 15207424, 158880768, 1801996288, 22088716288, 289379395584, 4040899657728, 60045059489792, 944460646318080, 15670973219667968, 273813250221277184, 5024207327266603008, 96554813072964845568 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..460

FORMULA

a(n) ~ c * d^n * n!, where d = 0.87361286073825385348141673848..., c = 1.678751353034864037734331900009... . - Vaclav Kotesovec, Aug 28 2014

MAPLE

b:= proc(u, o, t) option remember; `if`(u+o=0, 1,

      add(b(u+j-1, o-j, `if`(t=2, 3, 1)), j=1..o) +`if`(t<3,

      add(b(u-j, o+j-1, `if`(t=1, 2, 0)), j=1..u), 0))

    end:

a:= n-> b(n, 0, 0):

seq(a(n), n=0..30);  # Alois P. Heinz, Oct 07 2013

CROSSREFS

Column k=0 of A230797.

Column k=10 of A242784.

Sequence in context: A230797 A128652 A152316 * A152326 A152330 A152319

Adjacent sequences:  A177517 A177518 A177519 * A177521 A177522 A177523

KEYWORD

nonn

AUTHOR

R. H. Hardin, May 10 2010

EXTENSIONS

a(17)-a(22) from Alois P. Heinz, Oct 07 2013

STATUS

approved

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Last modified August 6 16:05 EDT 2020. Contains 336255 sequences. (Running on oeis4.)