A057812 Numbers k such that pi(k) is odd.

2, 5, 6, 11, 12, 17, 18, 23, 24, 25, 26, 27, 28, 31, 32, 33, 34, 35, 36, 41, 42, 47, 48, 49, 50, 51, 52, 59, 60, 67, 68, 69, 70, 73, 74, 75, 76, 77, 78, 83, 84, 85, 86, 87, 88, 97, 98, 99, 100, 103, 104, 105, 106, 109, 110, 111, 112, 127, 128, 129

Offset: 1

Author

N. J. A. Sloane, Nov 07 2000

Keywords

• nonn

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
• Ping Ngai Chung and Shiyu Li, On the residue classes of π(n) modulo t, INTEGERS: Electronic Journal of Combinatorial Number Theory 13 (2013), A79.

Crossrefs

Cf. A000720, A057811.

Programs

Mathematica

Position[Accumulate[Table[If[PrimeQ[n],1,0],{n,150}]],?OddQ]//Flatten (* _Harvey P. Dale, Jan 30 2019 *)

PARI

is(n)=primepi(n)%2 \\ Charles R Greathouse IV, Dec 19 2014

Formula

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