This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A177480 #26 Oct 02 2024 09:05:40
%S A177480 1,1,2,6,20,84,412,2300,14676,104536,825660,7168860,67826340,
%T A177480 695174208,7671602644,90700227700,1143825611348,15325929083336,
%U A177480 217429459642252,3256039887793868,51325896829151684,849518895902379696,14730333827970237220,267028337196612514596,5051094767395355339476
%N A177480 Number of permutations of order n avoiding the consecutive pattern egfh with e<f, e<h, g<f and g<h.
%C A177480 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.
%H A177480 S. Kitaev, <a href="https://doi.org/10.1016/j.dam.2006.09.011">Introduction to partially ordered patterns</a>, Discrete Applied Mathematics 155 (2007), 929-944.
%t A177480 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 *)
%Y A177480 Cf. A117156, A177470, A177471, A177472, A177473, A177475, A177476, A177477, A177478, A177479, A177481, A177482, A177483, A177484, A376694.
%K A177480 nonn
%O A177480 0,3
%A A177480 Signy Olafsdottir (signy06(AT)ru.is), May 09 2010
%E A177480 a(0), a(10)-a(14) from _Alois P. Heinz_, Mar 10 2020
%E A177480 a(15)-a(16) from _Giovanni Resta_, Mar 11 2020
%E A177480 Edited and a(17)-a(24) added by _Max Alekseyev_, Oct 01 2024