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A177476 Avoiding the pattern 231'1. To avoid 231'1 means not to have four consecutive letters such that if the third letter is removed, then in the obtained 3 letter word the smallest letter is the last one, and the largest letter is the second one. 2
1, 1, 2, 6, 20, 83, 402, 2245, 14192, 100650, 792508, 6859260, 64772648, 662630653, 7301841444, 86212535179, 1085834949064 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..16.

S. Kitaev, Introduction to partially ordered patterns, Discrete Applied Mathematics 155 (2007), 929-944.

MATHEMATICA

ok[{x_, y_, _, z_}] := Not[x>z && y>z && y>x]; a[n_] := Length@ Select[ Permutations@ Range@ n, AllTrue[ Partition[#, 4, 1], ok] &]; a /@ Range[0, 9]

CROSSREFS

Cf. A117156, A177470, A177471, A177472, A177473, A177474, A177475, A177477, A177478, A177479, A177480, A177481, A177482, A177483, A177484.

Sequence in context: A260788 A337274 A115084 * A266600 A177474 A177480

Adjacent sequences:  A177473 A177474 A177475 * A177477 A177478 A177479

KEYWORD

nonn,more

AUTHOR

Signy Olafsdottir (signy06(AT)ru.is), May 09 2010

EXTENSIONS

a(0), a(10)-a(14) from Alois P. Heinz, Mar 10 2020

a(15)-a(16) from Giovanni Resta, Mar 11 2020

STATUS

approved

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Last modified September 24 06:13 EDT 2021. Contains 347623 sequences. (Running on oeis4.)