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Search: id:A068050
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| A068050 |
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Number of values of k, 1<=k<=n, for which floor(n/k) is prime. |
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+0
2
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| 0, 1, 1, 1, 2, 2, 3, 2, 2, 4, 5, 3, 4, 5, 6, 5, 6, 5, 6, 6, 7, 9, 10, 6, 7, 9, 9, 9, 10, 10, 11, 9, 10, 12, 14, 11, 12, 13, 14, 13, 14, 13, 14, 14, 15, 17, 18, 13, 14, 16, 17, 18, 19, 17, 19, 18, 19, 21, 22, 18, 19, 20, 21, 19, 21, 22, 23, 23, 24, 26, 27, 21, 22, 23, 24, 24, 26, 27
(list; graph; listen)
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OFFSET
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1,5
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EXAMPLE
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a(10)=4 as floor(10/k) for k = 1 to 10 is 10,5,3,2,2,1,1,1,1,1, respectively; this is prime for k=2,3,4,5.
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MATHEMATICA
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a[n_] := Length[Select[Table[Floor[n/i], {i, 1, n}], PrimeQ]]
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CROSSREFS
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Cf. A067514.
Sequence in context: A160651 A086454 A069360 this_sequence A156220 A083900 A113517
Adjacent sequences: A068047 A068048 A068049 this_sequence A068051 A068052 A068053
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KEYWORD
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easy,nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Feb 12 2002
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EXTENSIONS
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Edited by Dean Hickerson (dean.hickerson(AT)yahoo.com), Feb 12 2002
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