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Number of unlabeled antichains of finite sets spanning n vertices with singleton edges allowed.
13

%I #15 Jul 26 2024 13:01:15

%S 1,1,4,18,142,3100,823042

%N Number of unlabeled antichains of finite sets spanning n vertices with singleton edges allowed.

%F a(n) = A304996(n) - A304996(n-1) for n > 0. - _Andrew Howroyd_, Aug 13 2019

%F Euler transform of A304983. - _Andrew Howroyd_, Aug 14 2019

%e Non-isomorphic representatives of the a(3) = 18 antichains:

%e {{1,2,3}}

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

%Y Cf. A006126, A261005, A304996, A304997, A304998, A304999, A305000, A305001.

%Y See also A374399.

%K nonn,more

%O 0,3

%A _Gus Wiseman_, May 23 2018

%E a(5)-a(6) from _Andrew Howroyd_, Aug 13 2019