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Search: id:A093890
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| A093890 |
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Number of primes arising as the sum of one or more divisors of n. |
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+0
5
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| 0, 2, 1, 4, 1, 5, 1, 6, 2, 7, 1, 9, 1, 5, 4, 11, 1, 12, 1, 13, 5, 5, 1, 17, 2, 5, 4, 16, 1, 20, 1, 18, 4, 6, 6, 24, 1, 5, 5, 24, 1, 24, 1, 18, 11, 5, 1, 30, 1, 15, 3, 18, 1, 30, 6, 30, 5, 7, 1, 39, 1, 3, 18, 31, 6, 34, 1, 16, 3, 34, 1, 44, 1, 4, 13, 16, 4, 39, 1, 42, 5, 5, 1, 48, 5, 5, 2, 41, 1, 51, 2
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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a(2^n) = pi(2^(n+1)-1).
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EXAMPLE
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a(4) = 4, the divisors of 4 are 1, 2 and 4.
Primes arising are 2, 3= 1+2, 5 = 1+4 and 7 = 1 + 2 + 4.
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MATHEMATICA
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Do[l = Subsets[Divisors[n]]; l = Union[Map[Plus @@ #&, l]]; Print[Length[Select[l, PrimeQ]]], {n, 100}] - Ryan Propper (rpropper(AT)stanford.edu), Jun 04 2006
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CROSSREFS
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Cf. A093891, A093892.
Adjacent sequences: A093887 A093888 A093889 this_sequence A093891 A093892 A093893
Sequence in context: A007104 A102627 A088296 this_sequence A006306 A083711 A018783
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KEYWORD
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nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Apr 23 2004
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EXTENSIONS
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Corrected and extended by Ryan Propper (rpropper(AT)stanford.edu), Jun 04 2006
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