This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A304997 #15 Jul 26 2024 13:01:15
%S A304997 1,1,4,18,142,3100,823042
%N A304997 Number of unlabeled antichains of finite sets spanning n vertices with singleton edges allowed.
%F A304997 a(n) = A304996(n) - A304996(n-1) for n > 0. - _Andrew Howroyd_, Aug 13 2019
%F A304997 Euler transform of A304983. - _Andrew Howroyd_, Aug 14 2019
%e A304997 Non-isomorphic representatives of the a(3) = 18 antichains:
%e A304997 {{1,2,3}}
%e A304997 {{3},{1,2}}
%e A304997 {{3},{1,2,3}}
%e A304997 {{1,3},{2,3}}
%e A304997 {{1},{2},{3}}
%e A304997 {{2},{3},{1,3}}
%e A304997 {{2},{3},{1,2,3}}
%e A304997 {{3},{1,2},{2,3}}
%e A304997 {{3},{1,3},{2,3}}
%e A304997 {{1,2},{1,3},{2,3}}
%e A304997 {{1},{2},{3},{2,3}}
%e A304997 {{1},{2},{3},{1,2,3}}
%e A304997 {{2},{3},{1,2},{1,3}}
%e A304997 {{2},{3},{1,3},{2,3}}
%e A304997 {{3},{1,2},{1,3},{2,3}}
%e A304997 {{1},{2},{3},{1,3},{2,3}}
%e A304997 {{2},{3},{1,2},{1,3},{2,3}}
%e A304997 {{1},{2},{3},{1,2},{1,3},{2,3}}
%Y A304997 Cf. A006126, A261005, A304996, A304997, A304998, A304999, A305000, A305001.
%Y A304997 See also A374399.
%K A304997 nonn,more
%O A304997 0,3
%A A304997 _Gus Wiseman_, May 23 2018
%E A304997 a(5)-a(6) from _Andrew Howroyd_, Aug 13 2019