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A177519 Number of permutations of 1..n avoiding adjacent step pattern up, down, down, up. 3
1, 2, 6, 24, 109, 588, 3654, 26125, 209863, 1876502, 18441367, 197776850, 2297242583, 28739304385, 385195455471, 5507210188401, 83657067537498, 1345556172013026, 22844387886649418, 408258252653717337, 7660885499702743124, 150600621665021781932 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..200

FORMULA

a(n) ~ c * d^n * n!, where d = 0.89356257576899599804435763285311831354458355576519..., c = 1.593348415562339201282264582915828860634166516332738... . - Vaclav Kotesovec, Aug 29 2014

MAPLE

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

      `if`(t<3, add(b(u+j-1, o-j, 1), j=1..o), 0)+

      add(b(u-j, o+j-1, `if`(t in [0, 3], 0, t+1)), j=1..u))

    end:

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

seq(a(n), n=1..30);  # Alois P. Heinz, Oct 07 2013

CROSSREFS

Column k=0 of A230695.

Column k=9 of A242784.

Sequence in context: A189840 A189255 A230695 * A214762 A141254 A216879

Adjacent sequences:  A177516 A177517 A177518 * A177520 A177521 A177522

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 April 18 16:32 EDT 2019. Contains 322209 sequences. (Running on oeis4.)