%I #29 Jul 06 2024 04:43:51
%S 2,4,11,31,309,1028,12251,43390,564163,28192750,105097565,5586502348,
%T 80316571436,305761713237,4461632979717,252252704148404,
%U 14458792895301660,55890484045084135,3249254387052557215,48995571600129458363,190499823401327905601
%N Number of primes < 2^prime(n).
%H Amiram Eldar, <a href="/A086690/b086690.txt">Table of n, a(n) for n = 1..24</a> (terms 1..23 from Gord Palameta)
%H Tomás Oliveira e Silva, <a href="https://sweet.ua.pt/tos/primes.html">Tables of values of pi(x) and of pi2(x)</a>.
%F a(n) = A007053(A000040(n)).
%F a(n) = A000720(A034785(n)). - _Amiram Eldar_, Jul 06 2024
%e There are 11 primes < 2^prime(3) = 2^5, so a(3) = 11.
%t Table[ PrimePi[ 2^Prime[n]], {n, 1, 14}]
%o (PARI) a(n) = primepi(2^prime(n));
%Y Cf. A000040, A000720, A007053, A034785.
%K nonn
%O 1,1
%A _Cino Hilliard_, Jul 28 2003
%E Extended by _Robert G. Wilson v_, Jul 30 2003
%E Revised by _Max Alekseyev_, Jul 20 2007