OFFSET
1,2
COMMENTS
A binary index of n (row n of A048793) is any position of a 1 in its reversed binary expansion. For example, 18 has reversed binary expansion (0,1,0,0,1) and binary indices {2,5}.
EXAMPLE
The terms together with the corresponding set-systems begin:
1: {{1}}
4: {{1,2}}
20: {{1,2},{1,3}}
52: {{1,2},{1,3},{2,3}}
64: {{1,2,3}}
68: {{1,2},{1,2,3}}
84: {{1,2},{1,3},{1,2,3}}
116: {{1,2},{1,3},{2,3},{1,2,3}}
308: {{1,2},{1,3},{2,3},{1,4}}
320: {{1,2,3},{1,4}}
324: {{1,2},{1,2,3},{1,4}}
340: {{1,2},{1,3},{1,2,3},{1,4}}
372: {{1,2},{1,3},{2,3},{1,2,3},{1,4}}
MATHEMATICA
bpe[n_]:=Join@@Position[Reverse[IntegerDigits[n, 2]], 1];
c=Table[Length[Union[Sort/@Tuples[bpe/@bpe[n]]]], {n, 10000}];
Select[Range[Length[c]], FreeQ[Take[c, #-1], c[[#]]]&]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Dec 16 2023
STATUS
approved