%N Number of digraphs with indegree = outdegree at each vertex, or Eulerian digraphs (including disconnected graphs) with n nodes.
%D F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 219 (but there is an error).
%D R. C. Read (rcread(AT)math.uwaterloo.ca), email to _N. J. A. Sloane_, 28 August, 2000.
%Y Euler transform of A058337.
%A _N. J. A. Sloane_.
%E a(7) added using A058337 by _Falk Hüffner_, Dec 03 2015
%E a(8) and a(9) added using A058337 by _Brendan McKay_, May 05 2019