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A177480
Number of permutations of order n avoiding the consecutive pattern egfh with e<f, e<h, g<f and g<h.
7
1, 1, 2, 6, 20, 84, 412, 2300, 14676, 104536, 825660, 7168860, 67826340, 695174208, 7671602644, 90700227700, 1143825611348, 15325929083336, 217429459642252, 3256039887793868, 51325896829151684, 849518895902379696, 14730333827970237220, 267028337196612514596, 5051094767395355339476
OFFSET
0,3
COMMENTS
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.
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 *)
KEYWORD
nonn
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
Edited and a(17)-a(24) added by Max Alekseyev, Oct 01 2024
STATUS
approved