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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

Table of n, a(n) for n=0..23.

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 * A196253 A338563 A345271

Adjacent sequences:  A220229 A220230 A220231 * A220233 A220234 A220235

KEYWORD

nonn

AUTHOR

Geoffrey Critzer, Dec 08 2012

STATUS

approved

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Last modified October 24 05:38 EDT 2021. Contains 348217 sequences. (Running on oeis4.)