Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #10 Jun 23 2024 22:02:42
%S 1,3,4,7,8,9,10,13,14,15,16,19,20,21,22,29,30,37,38,39,40,43,44,45,46,
%T 53,54,55,56,57,58,61,62,63,64,65,66,71,72,79,80,81,82,89,90,91,92,93,
%U 94,95,96,101,102,107,108,113,114,115,116,117,118,119
%N Numbers k such that pi(k) is even.
%H Charles R Greathouse IV, <a href="/A057811/b057811.txt">Table of n, a(n) for n = 1..10000</a>
%H Ping Ngai Chung and Shiyu Li, <a href="http://www.emis.de/journals/INTEGERS/papers/n79/n79.Abstract.html"> On the residue classes of π(n) modulo t</a>, INTEGERS: Electronic Journal of Combinatorial Number Theory 13 (2013), A79.
%F Chang & Li show that a(n) < 64n + o(1), and a(n) < 8n + o(1) under the Hardy-Littlewood prime tuples conjecture. - _Charles R Greathouse IV_, Dec 19 2014
%t Select[Range[120],EvenQ[PrimePi[#]]&] (* _Harvey P. Dale_, Apr 10 2024 *)
%o (PARI) is(n)=primepi(n)%2==0 \\ _Charles R Greathouse IV_, Dec 19 2014
%Y Cf. A000720, A057812.
%K nonn
%O 1,2
%A _N. J. A. Sloane_, Nov 07 2000