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%I #10 Mar 10 2020 19:27:29
%S 1,1,2,6,20,80,360,1888,11168,75168,560960,4632320,41627520,405993472,
%T 4256566784,47855992320,573443425280,7304885964800,98493107742720,
%U 1402190308089856,21008850635694080,330557870033510400,5448181151148032000,93883859983130624000
%N Suppose e<f, e<h, g<f and g<h. To avoid fegh means not to have four consecutive letters such that the second and the third letters are less than the first and the fourth letters.
%H Alois P. Heinz, <a href="/A177482/b177482.txt">Table of n, a(n) for n = 0..100</a>
%H 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.
%K nonn
%O 0,3
%A Signy Olafsdottir (signy06(AT)ru.is), May 09 2010
%E a(0)=1, a(10)-a(23) from _Alois P. Heinz_, Mar 10 2020
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