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Number of non-isomorphic connected set-systems covering n vertices with no singletons.
1

%I #5 Jan 31 2019 19:33:34

%S 1,0,1,6,171,611846,200253853704319,263735716028826427334553304608242,

%T 5609038300883759793482640992086670066496449147691597380632107520565546

%N Number of non-isomorphic connected set-systems covering n vertices with no singletons.

%C The labeled case is A323817.

%F Inverse Euler transform of A317795.

%e Non-isomorphic representatives of the a(3) = 6 set-systems:

%e {{1,2,3}}

%e {{1,3},{2,3}}

%e {{2,3},{1,2,3}}

%e {{1,2},{1,3},{2,3}}

%e {{1,3},{2,3},{1,2,3}}

%e {{1,2},{1,3},{2,3},{1,2,3}}

%Y Cf. A000295, A003465, A016031, A048143, A055621, A293510, A305001, A317795 (not necessarily connected), A323817 (unlabeled case), A323819 (with singletons).

%K nonn

%O 0,4

%A _Gus Wiseman_, Jan 30 2019