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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. 3
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
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
Sequence in context: A260788 A337274 A115084 * A266600 A177474 A177480
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 May 19 02:10 EDT 2024. Contains 372666 sequences. (Running on oeis4.)