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A220232 Number of rooted labeled trees of height 2 such that every leaf is at a distance 2 from the root. 1

%I

%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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Last modified November 29 15:46 EST 2021. Contains 349416 sequences. (Running on oeis4.)