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 A273652 #5 May 27 2016 11:33:57
%S A273652 2,9,30,90,255,693,1820,4644,11565,28215,67650,159822,372827,860265,
%T A273652 1966200,4456584,10027161,22413483,49807550,110100690,242221287,
%U A273652 530579709,1157628180,2516582700,5452595525,11777605983,25367150970,54492397974,116769423795
%N A273652 Number of forests of labeled rooted trees of height at most 1, with n labels, two of which are used for root nodes and any root may contain >= 1 labels.
%H A273652 Alois P. Heinz, <a href="/A273652/b273652.txt">Table of n, a(n) for n = 2..1000</a>
%F A273652 E.g.f.: x^2/2! * Sum_{j=0..2} Stirling2(2,j)*exp(x)^j.
%F A273652 a(n) = C(n,2) * Sum_{j=0..2} Stirling2(2,j) * j^(n-2).
%p A273652 a:= n-> binomial(n,2)*add(Stirling2(2,j)*j^(n-2), j=0..2):
%p A273652 seq(a(n), n=2..40);
%Y A273652 Column k=2 of A143396.
%K A273652 nonn
%O A273652 2,1
%A A273652 _Alois P. Heinz_, May 27 2016