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A177521 Number of permutations of 1..n avoiding adjacent step pattern up, down, up, up. 2
1, 2, 6, 24, 111, 612, 3906, 28701, 236527, 2167862, 21824925, 239861934, 2854894485, 36602472117, 502718236303, 7365503262033, 114653301213668, 1889769527067410, 32877891905367530, 602116339324675145, 11578253045158664158, 233244225298760907868 (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 = 0.91568163084580807076940792182223499091165..., c = 1.44100339681864767911275854344010332196608... . - 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, `if`(t=2, 3, 1)), j=1..o), 0)+

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

    end:

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

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

CROSSREFS

Columns k=11,13 of A242784.

Sequence in context: A046646 A174195 A274378 * A152322 A308726 A168490

Adjacent sequences:  A177518 A177519 A177520 * A177522 A177523 A177524

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 November 11 18:50 EST 2019. Contains 329031 sequences. (Running on oeis4.)