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A318128
Number of set-systems (finite sets of finite nonempty sets) with union {1,2,...,n} and intersection {}.
10
1, 0, 2, 84, 31478, 2147000136, 9223371998203475474, 170141183460469231537996491257596836636, 57896044618658097711785492504343953922551603929769020459976077632195066756398
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}]
KEYWORD
nonn
AUTHOR
Gus Wiseman, Aug 18 2018
STATUS
approved