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

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

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 * A370321 A196253 A338563

Adjacent sequences: A220229 A220230 A220231 * A220233 A220234 A220235

Keyword

nonn

Author

Geoffrey Critzer, Dec 08 2012

Status

approved