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*n-1), n=1..86); # Emeric Deutsch
MATHEMATICA
Table[PrimePi[2*n + 1], {n, 0, 100}] (* Wesley Ivan Hurt, Oct 02 2013 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Nov 19 2004
EXTENSIONS
More terms from Emeric Deutsch, Apr 12 2005
STATUS
approved