

A099801


PrimePi(2n+1), the number of primes less than or equal to 2n+1.


2



0, 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

0,2


COMMENTS

If we drop a(0), for all numbers k(n) [k(n) = 4*ceiling(n/2) + (1)^n] congruent to 1 or +1 (mod 4) starting with k(n) = {3,5,7,9,11,...}, a(k(n)) is the number of primes up to a(k(n)).  Daniel Forgues, Mar 01 2009
For n > 0, equals 1 (to account for the even prime 2 which is not congruent to 1 or +1 (mod 4)) + partial sums of A101264 (for n > 0).  Daniel Forgues, Mar 01 2009


LINKS

Daniel Forgues, Table of n, a(n) for n = 0..49999


MAPLE

with(numtheory):seq(pi(2*n1), n=1..86); # Emeric Deutsch


MATHEMATICA

Table[PrimePi[2*n + 1], {n, 0, 100}] (* Wesley Ivan Hurt, Oct 02 2013 *)


CROSSREFS

Bisection of A000720.
Sequence in context: A082288 A305397 A316627 * A099802 A196266 A112232
Adjacent sequences: A099798 A099799 A099800 * A099802 A099803 A099804


KEYWORD

nonn,easy


AUTHOR

N. J. A. Sloane, Nov 19 2004


EXTENSIONS

More terms from Emeric Deutsch, Apr 12 2005


STATUS

approved



