OFFSET
0,3
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..50
EXAMPLE
Non-isomorphic representatives of the a(3) = 10 set-systems:
{{1},{2},{3}}
{{1},{2},{1,2}}
{{1},{2},{1,3}}
{{1},{2},{1,2,3}}
{{1},{1,2},{1,3}}
{{1},{1,2},{2,3}}
{{1},{1,2},{1,2,3}}
{{1},{2,3},{1,2,3}}
{{1,2},{1,3},{2,3}}
{{1,2},{1,3},{1,2,3}}
MATHEMATICA
brute[m_]:=First[Sort[Table[Sort[Sort /@ (m/.Rule@@@Table[{(Union@@m)[[i]], p[[i]]}, {i, Length[p]}])], {p, Permutations[Range[Length[Union@@m]]]}]]];
Table[Length[Union[brute /@ Subsets[Subsets[Range[n], {1, n}], {n}]]], {n, 0, 4}]
PROG
(PARI) a(n) = polcoef(G(n, n), n) \\ G defined in A368186. - Andrew Howroyd, Jan 11 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jan 07 2024
EXTENSIONS
Terms a(6) and beyond from Andrew Howroyd, Jan 11 2024
STATUS
approved