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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
0, 0, 0, 6, 12, 80, 390, 2352, 15176, 106416, 801450, 6446000, 55056012, 497109912, 4726554014, 47164460280, 492470203920, 5366715030752, 60896862950994, 718023996605664, 8780720796483860, 111182108454527880, 1455411630641384262, 19668592336395304808
OFFSET
0,4
FORMULA
E.g.f.: x*(exp(x*(exp(x)-1))-1).
MATHEMATICA
nn=25; a=x (Exp[x]-1); Range[0, nn]! CoefficientList[Series[x (Exp[a]-1), {x, 0, nn}], x]
CROSSREFS
Cf. A000551.
Sequence in context: A239854 A061520 A305058 * A370321 A196253 A338563
KEYWORD
nonn
AUTHOR
Geoffrey Critzer, Dec 08 2012
STATUS
approved