|
| |
|
|
A119607
|
|
Number of primes of the form f(n) - 1, where f(n) is the product of one or more divisors of n.
|
|
0
|
|
|
|
0, 0, 1, 2, 0, 4, 0, 3, 1, 1, 0, 11, 0, 2, 1, 4, 0, 8, 0, 6, 1, 2, 0, 18, 0, 1, 1, 6, 0, 25, 0, 5, 1, 2, 0, 21, 0, 1, 1, 11, 0, 25, 0, 5, 1, 0, 0, 27, 0, 4, 1, 5, 0, 13, 0, 11, 1, 0, 0, 83, 0, 1, 1, 7, 0, 17, 0, 7, 1, 11, 0, 34, 0, 1, 1, 7, 0, 15, 0, 17, 1, 2, 0, 71, 0, 1, 1, 7, 0, 66, 0, 6, 1, 0, 0, 36
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,4
|
|
|
LINKS
|
Table of n, a(n) for n=1..96.
|
|
|
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 subtracting 1 yields {-1, 0, 1, 3, 1, 3, 7, 7}, of which the primes are {3, 7}.
|
|
|
MATHEMATICA
|
Do[l = Subsets[Divisors[n]]; l = Union[Map[Times @@ # - 1&, l]]; Print[Length[Select[l, PrimeQ]]], {n, 100}]
|
|
|
CROSSREFS
|
Sequence in context: A051517 A053118 A181481 * A164297 A109578 A082519
Adjacent sequences: A119604 A119605 A119606 * A119608 A119609 A119610
|
|
|
KEYWORD
|
nonn
|
|
|
AUTHOR
|
Ryan Propper (rpropper(AT)stanford.edu), Jun 04 2006
|
|
|
STATUS
|
approved
|
| |
|
|
