%I #20 Apr 29 2016 17:28:31
%S 2,2,16,504,52944,17294924,17347940328
%N Number of nonwellfounded sets or hypersets (sets that can contain themselves) of level n (representable by graphs with n nodes).
%H A. Casagrande, C. Piazza, A. Policriti, <a href="http://sets2015.cnam.fr/papers/00010001.pdf">Is hyperextensionality preservable under deletions of graph elements?</a>, Preprint 2015.
%H Christopher Tubbs et al., <a href="https://github.com/ctubbsii/hypersets">GitHub Hypersets Project</a> for generating integers in the sequence.
%K nonn,hard,more
%O 1,1
%A Elaine Milito (emilito(AT)bird.wcupa.edu)
%E a(6)a(7) from _Christopher Tubbs_, Oct 19 2013
