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A075084
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Number of composite numbers between n and 2n.
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0
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0, 1, 2, 3, 4, 5, 5, 7, 7, 7, 8, 9, 10, 12, 12, 12, 13, 15, 15, 17, 17, 17, 18, 19, 20, 21, 21, 22, 23, 24, 24, 26, 27, 27, 28, 28, 28, 30, 31, 31, 32, 33, 34, 36, 36, 37, 38, 40, 40, 41, 41, 41, 42, 43, 43, 44, 44, 45, 46, 48, 49, 51, 52, 52, 53, 53, 54, 56, 56, 56, 57, 59, 60
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| The number of composite numbers <= n is n less the number of primes less 1.
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FORMULA
| n - Pi(2n) + Pi(n-1) + 1. The sequence is nondecreasing.
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EXAMPLE
| a(8) = 7: the composite numbers are 8,9,10,12,14,15 and 16.
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MATHEMATICA
| Table[n - PrimePi[2n] + PrimePi[n - 1] + 1, {n, 2, 75}]
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CROSSREFS
| Sequence in context: A134875 A134889 A094802 * A086593 A073757 A088468
Adjacent sequences: A075081 A075082 A075083 * A075085 A075086 A075087
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KEYWORD
| easy,nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Sep 11 2002
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EXTENSIONS
| Edited by Robert G. Wilson v (rgwv(AT)rgwv.com), Sep 12 2002
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