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}}
64: {{1,2,3}}
20: {{1,2},{1,3}}
68: {{1,2},{1,2,3}}
52: {{1,2},{1,3},{2,3}}
84: {{1,2},{1,3},{1,2,3}}
308: {{1,2},{1,3},{2,3},{1,4}}
116: {{1,2},{1,3},{2,3},{1,2,3}}
820: {{1,2},{1,3},{2,3},{1,4},{2,4}}
372: {{1,2},{1,3},{2,3},{1,2,3},{1,4}}
884: {{1,2},{1,3},{2,3},{1,2,3},{1,4},{2,4}}
MATHEMATICA
nn=10000;
bpe[n_]:=Join@@Position[Reverse[IntegerDigits[n, 2]], 1];
dd=Select[Range[nn], Max@@First/@FactorInteger[#]<=3&];
qq=Table[Length[Tuples[bpe/@bpe[n]]], {n, nn}];
kk=Select[Range[Length[dd]], SubsetQ[qq, Take[dd, #]]&]
Table[Position[qq, dd[[n]]][[1, 1]], {n, kk}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Dec 17 2023
STATUS
approved