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 A037184 #11 Dec 15 2020 17:53:33 %S A037184 6,48,420,3840,38010,407904,4739112,59405760,800309070,11542072080, %T A037184 177536452236,2902434644928,50271450894210,919799178083520, %U A037184 17730187503894480,359183503307677824,7629999730919490582,169605272611054951920,3937616869933172881140 %N A037184 Functional digraphs with 1 node not in the image. %C A037184 Comment from _Christian G. Bower_: Labeled graphs where every node has outdegree 1, one node has indegree 0, one node has indegree 2, all other nodes have indegree 1 and there are no loops of length 1. %F A037184 a(n) = n * ( (n-2)*a(n-1) + (n-1)*a(n-2) ) / (n-3). %F A037184 E.g.f.: x^3 / ((1-x)^3 * e^x). %Y A037184 A000166 (derangements) gives number of functional digraphs with all nodes in the range, A007778 gives number of functional digraphs with n nodes. %K A037184 easy,nonn %O A037184 3,1 %A A037184 _Erich Friedman_