OFFSET
0,3
FORMULA
Inverse binomial transform of A318129.
EXAMPLE
The a(2) = 2 set-systems are {{1},{2}}, and {{1},{2},{1,2}}.
MATHEMATICA
Table[Length[Select[Subsets[Rest[Subsets[Range[n]]]], And[Union@@#===Range[n], Intersection@@#=={}]&]], {n, 4}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Aug 18 2018
STATUS
approved