A177480 Number of permutations of order n avoiding the consecutive pattern egfh with e

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

Author

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

Keywords

• nonn

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.

Crossrefs

Cf. A117156, A177470, A177471, A177472, A177473, A177475, A177476, A177477, A177478, A177479, A177481, A177482, A177483, A177484, A376694.

Programs

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 *)

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