A120309 Numbers k such that pi(k) == 0 (mod 4), where pi() = A000720.

1, 7, 8, 9, 10, 19, 20, 21, 22, 37, 38, 39, 40, 53, 54, 55, 56, 57, 58, 71, 72, 89, 90, 91, 92, 93, 94, 95, 96, 107, 108, 131, 132, 133, 134, 135, 136, 151, 152, 153, 154, 155, 156, 173, 174, 175, 176, 177, 178, 193, 194, 195, 196

Offset: 1

Author

Roger L. Bagula, Jun 20 2006

Keywords

• nonn

Crossrefs

Cf. A000720.

Programs

Mathematica

a = Flatten[Table[If[Mod[PrimePi[n], 4] == 0, n, {}], {n, 1, 200}]]
Select[Range[200],Mod[PrimePi[#],4]==0&] (* Harvey P. Dale, Jul 20 2024 *)

PARI

isok(k) = (primepi(k) % 4) == 0; \\ Michel Marcus, Feb 09 2021

Extensions

Edited by N. J. A. Sloane, Jul 22 2006