login
A207329
Number of distinct integers which can be represented as the product of factors of n, using each factor at most once.
2
1, 2, 2, 4, 2, 7, 2, 7, 4, 7, 2, 20, 2, 7, 7, 11, 2, 20, 2, 20, 7, 7, 2, 45, 4, 7, 7, 20, 2, 59, 2, 16, 7, 7, 7, 66, 2, 7, 7, 45, 2, 59, 2, 20, 20, 7, 2, 86, 4, 20, 7, 20, 2, 45, 7, 45, 7, 7, 2, 269, 2, 7, 20, 22, 7, 59, 2, 20, 7, 59, 2, 157, 2, 7, 20, 20, 7
OFFSET
1,2
COMMENTS
a(n) depends only on the prime signature of n.
LINKS
FORMULA
For prime p, a(p^n) = A000124(n) (independently of p).
a(n) = A069625(n) + 1. - Michel Marcus, Sep 17 2013
EXAMPLE
For n=4, n has factors 1, 2, and 4, which can be multiplied to yield 1, 2, 4, or 8, thus a(4)=4.
MATHEMATICA
a[n_] := Length[DeleteDuplicates[Times @@@ Subsets[Divisors[n]]]]; Table[a[n], {n, 100}]
CROSSREFS
Sequence in context: A325683 A331121 A057767 * A348219 A122977 A275870
KEYWORD
nonn
AUTHOR
Ben Branman, Feb 27 2012
STATUS
approved