A086690 Number of primes < 2^prime(n).

2, 4, 11, 31, 309, 1028, 12251, 43390, 564163, 28192750, 105097565, 5586502348, 80316571436, 305761713237, 4461632979717, 252252704148404, 14458792895301660, 55890484045084135, 3249254387052557215, 48995571600129458363, 190499823401327905601

Offset: 1

Author

Cino Hilliard, Jul 28 2003

Keywords

• nonn

Examples

			There are 11 primes < 2^prime(3) = 2^5, so a(3) = 11.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..24 (terms 1..23 from Gord Palameta)
• Tomás Oliveira e Silva, Tables of values of pi(x) and of pi2(x).

Crossrefs

Cf. A000040, A000720, A007053, A034785.

Programs

Mathematica

Table[ PrimePi[ 2^Prime[n]], {n, 1, 14}]

PARI

a(n) = primepi(2^prime(n));

Formula

a(n) = A007053(A000040(n)).

a(n) = A000720(A034785(n)). - Amiram Eldar, Jul 06 2024

Extensions

Extended by Robert G. Wilson v, Jul 30 2003

Revised by Max Alekseyev, Jul 20 2007