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 A128406 #13 Jun 21 2021 16:27:42
%S A128406 1,8,192,16384,5242880,6442450944,30786325577728,576460752303423488,
%T A128406 42501298345826806923264,12379400392853802748991242240,
%U A128406 14278816360970775978458864905355264,65334214448820184984967924626899496599552,1187470080331358621040493926581979953470445191168
%N A128406 a(n) = (n+1)*2^(n*(n+1)).
%C A128406 Hankel transform of A069723.
%C A128406 With offset 1, a(n) is the number of vertices with in-degree = 0 over all labeled digraphs (with self loops allowed) on n vertices. Equivalently, the number of elements in all labeled relations on an n-set that have no preimage. - _Geoffrey Critzer_, Aug 16 2016
%F A128406 a(n) = A095340(n)*A006125(n+1).
%t A128406 Table[n 2^(n - 1) 2^(n - 1)^2, {n, 1, 10}]
%t A128406 Table[(n+1)2^(n(n+1)),{n,0,20}] (* _Harvey P. Dale_, Jun 21 2021 *)
%Y A128406 Cf. A006125, A069723, A095340.
%K A128406 easy,nonn
%O A128406 0,2
%A A128406 _Paul Barry_, Mar 01 2007