A048989 Numbers k such that pi(k) is prime.

3, 4, 5, 6, 11, 12, 17, 18, 31, 32, 33, 34, 35, 36, 41, 42, 59, 60, 67, 68, 69, 70, 83, 84, 85, 86, 87, 88, 109, 110, 111, 112, 127, 128, 129, 130, 157, 158, 159, 160, 161, 162, 179, 180, 191, 192, 211, 212, 213, 214, 215, 216, 217, 218, 219

Offset: 1

Author

G. L. Honaker, Jr.

Keywords

• nonn
• easy
• nice

Comments

A000720(a(n)) is prime. - Omar E. Pol, Dec 19 2008

Links

• T. D. Noe, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000720.

Programs

Mathematica

Select[Range[250],PrimeQ[PrimePi[#]]&]  (* Harvey P. Dale, Mar 23 2011 *)

PARI

isok(k) = isprime(primepi(k)); \\ Michel Marcus, Jan 15 2023