A214195 Numbers with the number of distinct prime factors a multiple of 3.

1, 30, 42, 60, 66, 70, 78, 84, 90, 102, 105, 110, 114, 120, 126, 130, 132, 138, 140, 150, 154, 156, 165, 168, 170, 174, 180, 182, 186, 190, 195, 198, 204, 220, 222, 228, 230, 231, 234, 238, 240, 246, 252, 255, 258, 260, 264, 266, 270, 273, 276, 280, 282, 285

Offset: 1

Author

Enrique Pérez Herrero, Jul 07 2012

Keywords

• nonn

Comments

If GCD(a(n),a(m))=1, then a(n)*a(m) is also in this sequence. - Enrique Pérez Herrero, Nov 23 2013

Links

• Enrique Pérez Herrero, Table of n, a(n) for n = 1..5000

Crossrefs

Subsequences include A033992, A067885, A007304 and A147573.

Cf. A145784, A030230, A030231.

Programs

Mathematica

Select[Range[1000],Mod[PrimeNu[#],3]==0&]

PARI

is(n)=omega(n)%3==0 \\ Charles R Greathouse IV, Sep 14 2015

Formula

A010872(A001221(a(n))) = 0.