OFFSET
1,2
EXAMPLE
The divisors of 4 are D = {1, 2, 4} and the subsets of D are {{}, {1}, {2}, {4}, {1, 2}, {1, 4}, {2, 4}, {1, 2, 4}}. Taking the product of elements in these subsets and adding 1 yields {1, 2, 3, 5, 3, 5, 9, 9}, of which the primes are {2, 3, 5}.
MATHEMATICA
Do[l = Subsets[Divisors[n]]; l = Union[Map[Times @@ # + 1&, l]]; Print[Length[Select[l, PrimeQ]]], {n, 100}]
CROSSREFS
KEYWORD
dead
AUTHOR
Ryan Propper, Jun 04 2006
STATUS
approved