OFFSET
0,2
COMMENTS
These are sets that are closed under taking the quotient of two (not necessarily distinct) divisible terms.
FORMULA
For n > 0, a(n) = A326078(n) + 1.
EXAMPLE
The a(0) = 1 through a(5) = 17 subsets:
{} {} {} {} {} {}
{1} {1} {1} {1} {1}
{1,2} {1,2} {1,2} {1,2}
{1,3} {1,3} {1,3}
{1,2,3} {1,4} {1,4}
{1,2,3} {1,5}
{1,2,4} {1,2,3}
{1,3,4} {1,2,4}
{1,2,3,4} {1,2,5}
{1,3,4}
{1,3,5}
{1,4,5}
{1,2,3,4}
{1,2,3,5}
{1,2,4,5}
{1,3,4,5}
{1,2,3,4,5}
MATHEMATICA
Table[Length[Select[Subsets[Range[n]], SubsetQ[#, Select[Divide@@@Tuples[#, 2], IntegerQ]]&]], {n, 0, 10}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jun 04 2019
EXTENSIONS
Terms a(21) and beyond from Andrew Howroyd, Aug 30 2019
STATUS
approved