A064040 Integers whose number of distinct prime divisors is prime.

6, 10, 12, 14, 15, 18, 20, 21, 22, 24, 26, 28, 30, 33, 34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 48, 50, 51, 52, 54, 55, 56, 57, 58, 60, 62, 63, 65, 66, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 82, 84, 85, 86, 87, 88, 90, 91, 92, 93, 94, 95, 96, 98, 99, 100, 102, 104, 105

Offset

1,1

Comments

For all terms below 210 this sequence and A024619 are identical.

Links

Harry J. Smith, Table of n, a(n) for n = 1..1000

Example

210 = 2*3*5*7 has 4 prime factors, hence it is not here, but it is part of A024619.

Maple

q:= n-> isprime(nops(ifactors(n)[2])):
select(q, [$1..210])[];  # Alois P. Heinz, Apr 18 2024

Mathematica

Select[Range[200], PrimeQ[PrimeNu[#]] &] (* Paolo Xausa, Mar 28 2024 *)

Prog

(PARI) n=0; for (m=1, 10^9, if (isprime(omega(m)), write("b064040.txt", n++, " ", m); if (n==1000, break))) \\ Harry J. Smith, Sep 06 2009
(PARI) is(n)=isprime(omega(n)) \\ Charles R Greathouse IV, Sep 18 2015

Crossrefs

Cf. A001221, A024619, A000977, A033992, A007774, A033993, A051270, A063989.

Sequence in context: A348718 A325265 A105642 * A168638 A024619 A361102

Adjacent sequences: A064037 A064038 A064039 * A064041 A064042 A064043

Keyword

nonn,easy,changed

Author

Lior Manor, Aug 23 2001

Extensions

Edited by Charles R Greathouse IV, Mar 18 2010

Name edited by Michel Marcus, Oct 16 2023

Status

approved