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%I M2689 #24 May 12 2022 17:12:24
%S 1,3,7,24,117,663,4824,40367,381554,4001849,46043780,576018785,
%T 7783281188,112953364381,1752128923245,28930230194371,506596534953769
%N Number of 2-diregular connected digraphs with n nodes.
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H M. V. S. Ramanath & T. R. Walsh, <a href="/A005641/a005641.pdf">Enumeration and generation of a class of regular digraphs</a>, J. Graph Theory 11 (1987), no. 4, 471-479. (Annotated scanned copy)
%H R. J. Mathar, <a href="/A005642/a005642.pdf">Illustrations</a>
%Y Cf. A005641 (not necess. connected), A306892 (multiarcs allowed). Labeled version is A123544.
%K nonn
%O 2,2
%A _N. J. A. Sloane_
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