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%I #9 Dec 10 2012 00:02:00
%S 0,0,0,6,12,80,390,2352,15176,106416,801450,6446000,55056012,
%T 497109912,4726554014,47164460280,492470203920,5366715030752,
%U 60896862950994,718023996605664,8780720796483860,111182108454527880,1455411630641384262,19668592336395304808
%N Number of rooted labeled trees of height 2 such that every leaf is at a distance 2 from the root.
%F E.g.f.: x*(exp(x*(exp(x)-1))-1).
%t nn=25; a=x (Exp[x]-1); Range[0,nn]! CoefficientList[Series[x (Exp[a]-1), {x,0,nn}], x]
%Y Cf. A000551.
%K nonn
%O 0,4
%A _Geoffrey Critzer_, Dec 08 2012
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