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 A273653 #4 May 27 2016 11:40:54
%S A273653 5,40,220,1040,4550,19040,77448,308640,1209450,4668400,17766892,
%T A273653 66718288,247397150,906584000,3285842960,11788924992,41902786770,
%U A273653 147668053200,516315206260,1792304871280,6180666260230,21184488791840,72205377800600,244837696095200
%N A273653 Number of forests of labeled rooted trees of height at most 1, with n labels, three of which are used for root nodes and any root may contain >= 1 labels.
%H A273653 Alois P. Heinz, <a href="/A273653/b273653.txt">Table of n, a(n) for n = 3..1000</a>
%F A273653 E.g.f.: x^3/3! * Sum_{j=0..3} Stirling2(3,j)*exp(x)^j.
%F A273653 a(n) = C(n,3) * Sum_{j=0..3} Stirling2(3,j) * j^(n-3).
%p A273653 a:= n-> binomial(n,3)*add(Stirling2(3,j)*j^(n-3), j=0..3):
%p A273653 seq(a(n), n=3..40);
%Y A273653 Column k=3 of A143396.
%K A273653 nonn
%O A273653 3,1
%A A273653 _Alois P. Heinz_, May 27 2016