This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A220232 #9 Dec 10 2012 00:02:00
%S A220232 0,0,0,6,12,80,390,2352,15176,106416,801450,6446000,55056012,
%T A220232 497109912,4726554014,47164460280,492470203920,5366715030752,
%U A220232 60896862950994,718023996605664,8780720796483860,111182108454527880,1455411630641384262,19668592336395304808
%N A220232 Number of rooted labeled trees of height 2 such that every leaf is at a distance 2 from the root.
%F A220232 E.g.f.: x*(exp(x*(exp(x)-1))-1).
%t A220232 nn=25; a=x (Exp[x]-1); Range[0,nn]! CoefficientList[Series[x (Exp[a]-1), {x,0,nn}], x]
%Y A220232 Cf. A000551.
%K A220232 nonn
%O A220232 0,4
%A A220232 _Geoffrey Critzer_, Dec 08 2012