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 A197927 #32 Apr 03 2023 15:15:17
%S A197927 0,1,4,48,2048,327680,201326592,481036337152,4503599627370496,
%T A197927 166020696663385964544,24178516392292583494123520,
%U A197927 13944156602510523416463735259136,31901471898837980949691369446728269824,289909687580898100839964337544428699577745408
%N A197927 The number of isolated nodes in all labeled directed graphs (with self loops allowed) on n nodes.
%C A197927 Here, isolated means indegree = outdegree = 0.
%C A197927 a(n) is also the number of directed graphs on [n] (no self loops allowed, A053763) with a distinguished vertex of indegree 0. - _Geoffrey Critzer_, Apr 01 2023
%F A197927 E.g.f.: x*A(x) where A(x) = Sum_{n>=0} 2^(n^2)*x^n/n!.
%F A197927 a(n) = n * 2^((n-1)^2) = n*A002416(n-1).
%F A197927 Sum_{n>=0} a(n)*z^n/B(n) = z*Sum_{n>=0} A053763(n)*z^n/B(n) where B(n) = n!*2^binomial(n,2). - _Geoffrey Critzer_, Apr 01 2023
%t A197927 a = Sum[2^(n^2)x^n/n!, {n,0,20}]; Range[0,12]! CoefficientList[Series[x a, {x,0,12}], x]
%Y A197927 Cf. A011266, A053763, A002416.
%K A197927 nonn
%O A197927 0,3
%A A197927 _Geoffrey Critzer_, Oct 19 2011