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}}
7: {{1},{2},{1,2}}
20: {{1,2},{1,3}}
68: {{1,2},{1,2,3}}
320: {{1,2,3},{1,4}}
352: {{2,3},{1,2,3},{1,4}}
1088: {{1,2,3},{1,2,4}}
3136: {{1,2,3},{1,2,4},{3,4}}
5184: {{1,2,3},{1,2,4},{1,3,4}}
13376: {{1,2,3},{1,2,4},{1,3,4},{2,3,4}}
16704: {{1,2,3},{1,4},{1,2,3,4}}
17472: {{1,2,3},{1,2,4},{1,2,3,4}}
70720: {{1,2,3},{1,2,4},{1,3,4},{1,5}}
82240: {{1,2,3},{1,4},{1,2,3,4},{1,5}}
MATHEMATICA
bpe[n_]:=Join@@Position[Reverse[IntegerDigits[n, 2]], 1];
c=Table[Length[Select[Tuples[bpe/@bpe[n]], UnsameQ@@#&]], {n, 1000}];
Select[Range[Length[c]], FreeQ[Take[c, #-1], c[[#]]]&]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Dec 16 2023
STATUS
approved