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A101909 Number of primes between 2n and 4n. 4
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; text; internal format)
OFFSET

1,2

LINKS

T. D. Noe and Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

MATHEMATICA

f[n_] := PrimePi[4n] - PrimePi[2n]; Table[ f[n], {n, 76}] (* Robert G. Wilson v, Feb 10 2005 *)

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", ") ) }

(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

CROSSREFS

Cf. A101947, A101983, A101984, A101985.

Sequence in context: A259981 A070705 A216326 * A215676 A130872 A087627

Adjacent sequences:  A101906 A101907 A101908 * A101910 A101911 A101912

KEYWORD

easy,nonn

AUTHOR

Cino Hilliard, Jan 28 2005

STATUS

approved

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Last modified April 23 14:15 EDT 2019. Contains 322386 sequences. (Running on oeis4.)