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A101909
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Number of primes between 2n and 4n.
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5
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1, 2, 2, 2, 4, 4, 3, 5, 4, 4, 6, 6, 6, 7, 7, 7, 8, 9, 9, 10, 10, 9, 10, 9, 10, 12, 12, 13, 14, 13, 12, 13, 14, 13, 15, 14, 13, 15, 15, 15, 16, 16, 16, 17, 17, 18, 18, 19, 19, 21, 20, 19, 20, 19, 18, 19, 19, 20, 21, 22, 23, 23, 24, 23, 24, 24, 24, 26, 25, 25, 27, 27, 27, 28, 27, 26
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OFFSET
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1,2
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LINKS
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FORMULA
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MAPLE
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numtheory[pi](4*n)-numtheory[pi](2*n) ;
end proc:
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MATHEMATICA
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f[n_] := PrimePi[4n] - PrimePi[2n]; Table[ f[n], {n, 76}] (* Robert G. Wilson v, Feb 10 2005 *)
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PROG
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(PARI) bet2n4n(n) = { local(c, x, y); forstep(x=2, n, 2, c=0; forprime(y=x+1, x+x-1, c++; ); print1(c", ") ) }
(PARI) s=0; vector(100, n, s+=isprime(4*n-1)+isprime(4*n-3)-isprime(2*n-1)) \\ Charles R Greathouse IV, Mar 12 2012
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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