OFFSET
0,3
EXAMPLE
The a(2) = 3 sets of sets are {}, {{1},{2}}, {{1},{2},{1,2}}.
MATHEMATICA
Table[Length[Select[Subsets[Rest[Subsets[Range[n]]]], Or[#=={}, Intersection@@#=={}]&]], {n, 0, 4}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Aug 18 2018
STATUS
approved