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 A144208 #13 Feb 10 2015 08:42:12
%S A144208 1,1,1,2,17,221,3261,54801,1049235,22695027,548904831,14701691121,
%T A144208 432342705351,13856514927207,480891887472585,17971038945463101,
%U A144208 719613541474095591,30743125693699501431,1395902175504288127695
%N A144208 Number of simple graphs on n labeled nodes, where each maximally connected subgraph consists of a single node or has a unique cycle of length 3; also row sums of A144207.
%H A144208 Alois P. Heinz, <a href="/A144208/b144208.txt">Table of n, a(n) for n = 0..150</a>
%F A144208 a(n) = Sum_{k=0..n} A144207(n,k).
%F A144208 a(n) ~ c * n^(n-1), where c = 0.762590842281789937101466... . - _Vaclav Kotesovec_, Sep 10 2014
%e A144208 a(3) = 2, because there are 2 simple graphs on 3 labeled nodes, where each maximally connected subgraph consists of a single node or has a unique cycle of length 3:
%e A144208 .1.2. .1-2.
%e A144208 ..... .|/..
%e A144208 .3... .3...
%p A144208 T:= proc(n,k) option remember; if k=0 then 1 elif k<0 or n<k then 0 elif k=n then binomial(n-1,2) *n^(n-3) else T(n-1,k) +add(binomial(n-1,j) * T(j+1,j+1) *T(n-1-j,k-j-1), j=2..k-1) fi end: a:= n-> add(T(n,k), k=0..n): seq(a(n), n=0..23);
%t A144208 T[n_, k_] := T[n, k] = Which[k == 0, 1, k<0 || n<k, 0, k == n, Binomial[n-1, 2] *n^(n-3), True, T[n-1, k] + Sum[Binomial[n-1, j] * T[j+1, j+1] * T[n-1-j, k-j-1], {j, 2, k-1}]]; a[n_] := Sum[T[n, k], {k, 0, n}]; Table[a[n], {n, 0, 23}] (* _Jean-François Alcover_, Feb 05 2015, after _Alois P. Heinz_ *)
%Y A144208 Row sums of triangle A144207. A column of A144212. Cf. A053507, A007318.
%K A144208 nonn
%O A144208 0,4
%A A144208 _Alois P. Heinz_, Sep 14 2008