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A075699
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Number of primes in the interval (n,4n].
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2
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2, 3, 3, 4, 5, 6, 5, 7, 7, 8, 9, 10, 9, 10, 11, 12, 12, 13, 13, 14, 15, 15, 15, 15, 16, 18, 19, 20, 20, 20, 19, 20, 21, 21, 23, 23, 22, 24, 24, 25, 25, 26, 25, 26, 27, 28, 27, 28, 29, 31, 31, 31, 31, 31, 31, 32, 33, 34, 34, 35, 35, 35, 36, 36, 37, 38, 37, 39, 39, 40, 41, 41, 40
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OFFSET
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1,1
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COMMENTS
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Difference a(n+1)-a(n) = -1,0,1,2.
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LINKS
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FORMULA
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EXAMPLE
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a(4) = 4 because between 4 and 16 there are 4 primes: 5, 7, 11, 13.
a(7) = 5 because between 7 and 28 there are 5 primes: 11, 13, 17, 19, 23.
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MAPLE
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numtheory[pi](4*n)-numtheory[pi](n) ;
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MATHEMATICA
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s=4; a[n_] := PrimePi[s*n]-PrimePi[n]
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PROG
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(PARI) a(n) = primepi(4*n) - primepi(n); \\ Michel Marcus, Oct 02 2013
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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