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 A007108 M4667 #23 Dec 19 2021 04:28:34 %S A007108 0,0,0,1,9,216,7560,357120,22025430,1720751760,166198926600, %T A007108 19453788144000,2714247736061400,445133524289731200, %U A007108 84788348720139464400,18565341317290193025600,4631048864538293219022000,1305644758257711732981120000,413133912085072442199311376000 %N A007108 Number of connected labeled 2-regular digraphs with n nodes. %C A007108 From _R. J. Mathar_, Apr 29 2019: (Start) %C A007108 The numbers of labeled 2-regular digraphs with n >= 1 nodes and 1 <= k <= n components are %C A007108 0; %C A007108 0, 0; %C A007108 1, 0, 0; %C A007108 9, 0, 0, 0; %C A007108 216, 0, 0, 0, 0; %C A007108 7560, 10, 0, 0, 0, 0; %C A007108 357120, 315, 0, 0, 0, 0, 0; %C A007108 22025430, 14931, 0, 0, 0, 0, 0, 0; %C A007108 1720751760, 879984, 280, 0, 0, 0, 0, 0, 0; %C A007108 ... %C A007108 with row sums A007107. (End) %D A007108 R. W. Robinson, personal communication. %D A007108 R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1982. %D A007108 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A007108 Alois P. Heinz, <a href="/A007108/b007108.txt">Table of n, a(n) for n = 0..253</a> (first 49 terms from R. W. Robinson) %Y A007108 Cf. A007107 (EXP-transform). %K A007108 nonn,nice %O A007108 0,5 %A A007108 _N. J. A. Sloane_