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

1,2

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

Formula

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

Mathematica

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

Prog

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

Crossrefs

Subsequences include A033992, A067885, A007304 and A147573.

Cf. A145784, A030230, A030231.

Sequence in context: A114816 A299991 A000977 * A033992 A360525 A308127

Adjacent sequences: A214192 A214193 A214194 * A214196 A214197 A214198

Keyword

nonn

Author

Enrique Pérez Herrero, Jul 07 2012

Status

approved