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A101909
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Number of primes between 2n and 4n.
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4
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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LINKS
| T. D. Noe, Table of n, a(n) for n=1..1000
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MATHEMATICA
| f[n_] := PrimePi[4n] - PrimePi[2n]; Table[ f[n], {n, 76}] (from Robert G. Wilson v Feb 10 2005)
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PROG
| (PARI) bet2n4n(n) = { local(c, x, y); forstep(x=2, n, 2, c=0; forprime(y=x+1, x+x-1, c++; ); print1(c", ") ) }
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CROSSREFS
| Cf. A101947, A101983, A101984, A101985.
Sequence in context: A172309 A130453 A070705 * A130872 A087627 A195051
Adjacent sequences: A101906 A101907 A101908 * A101910 A101911 A101912
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KEYWORD
| easy,nonn
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AUTHOR
| Cino Hilliard (hillcino368(AT)gmail.com), Jan 28 2005
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