A099802 Bisection of A000720.

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

Offset: 1

Author

N. J. A. Sloane, Nov 19 2004

Keywords

• nonn
• easy

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. - Juri-Stepan Gerasimov, Oct 29 2009

Crossrefs

Cf. A099081.

Programs

Maple

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

PARI

a(n)=primepi(2*n) \\ Charles R Greathouse IV, Sep 02 2015

Sage

[prime_pi(2*n) for n in range(1, 75)] # Zerinvary Lajos, Jun 06 2009

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

Extensions

More terms from Emeric Deutsch, Apr 12 2005