
1, 2, 3, 4, 4, 5, 6, 6, 7, 8, 8, 9, 9, 9, 10, 11, 11, 11, 12, 12, 13, 14, 14, 15, 15, 15, 16, 16, 16, 17, 18, 18, 18, 19, 19, 20, 21, 21, 21, 22, 22, 23, 23, 23, 24, 24, 24, 24, 25, 25, 26, 27, 27, 28, 29, 29, 30, 30, 30, 30, 30, 30, 30, 31, 31, 32, 32, 32, 33, 34, 34, 34, 34, 34
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OFFSET

1,2


COMMENTS

Maximal number of primes possible in a string of 2n consecutive numbers.  Lekraj Beedassy, Dec 04 2004
a(n) = A139325(n,1) + 1.  Reinhard Zumkeller, Apr 14 2008
Or the number of primes <= 2n.  JuriStepan Gerasimov, Oct 29 2009


LINKS

Table of n, a(n) for n=1..74.


FORMULA

a(n) = A000720(n) + A035250(n)  A010051(n).  Reinhard Zumkeller, Jul 05 2010
a(n) = A000720(2*n).  Wesley Ivan Hurt, Jun 16 2013


MAPLE

with(numtheory):seq(pi(2*n), n=1..86); # Emeric Deutsch, Apr 12 2005


PROG

(Sage) [prime_pi(2*n) for n in range(1, 75)] # Zerinvary Lajos, Jun 06 2009
(PARI) a(n)=primepi(2*n) \\ Charles R Greathouse IV, Sep 02 2015


CROSSREFS

Cf. A099081.
Sequence in context: A305397 A316627 A099801 * A196266 A112232 A168389
Adjacent sequences: A099799 A099800 A099801 * A099803 A099804 A099805


KEYWORD

nonn,easy


AUTHOR

N. J. A. Sloane, Nov 19 2004


EXTENSIONS

More terms from Emeric Deutsch, Apr 12 2005


STATUS

approved

