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A177480 Suppose e<f, e<h, g<f and g<h. To avoid egfh means not to have four consecutive letters such that the first and the second letters are less than the third and the fourth letters. 2
1, 1, 2, 6, 20, 84, 412, 2300, 14676, 104536, 825660, 7168860, 67826340, 695174208, 7671602644, 90700227700, 1143825611348 (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[{e_, f_, g_, h_}] := e > g || e > h || f > g || f > h; a[n_] := Length@ Select[ Permutations[Range@n], AllTrue[ Partition[#, 4, 1], ok] &]; a /@ Range[0, 9] (* Giovanni Resta, Mar 11 2020 *)
CROSSREFS
Sequence in context: A177476 A266600 A177474 * A365229 A089179 A177483
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 March 28 10:55 EDT 2024. Contains 371241 sequences. (Running on oeis4.)