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Search: id:A119607
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| A119607 |
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Number of primes of the form f(n) - 1, where f(n) is the product of one or more divisors of n. |
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+0
1
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| 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; listen)
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OFFSET
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1,4
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EXAMPLE
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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}.
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MATHEMATICA
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Do[l = Subsets[Divisors[n]]; l = Union[Map[Times @@ # - 1&, l]]; Print[Length[Select[l, PrimeQ]]], {n, 100}]
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CROSSREFS
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Sequence in context: A102392 A051517 A053118 this_sequence A109578 A082519 A035688
Adjacent sequences: A119604 A119605 A119606 this_sequence A119608 A119609 A119610
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KEYWORD
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nonn
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AUTHOR
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Ryan Propper (rpropper(AT)stanford.edu), Jun 04 2006
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