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A214195 Numbers with the number of distinct prime factors a multiple of 3. 1
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 (list; graph; refs; listen; history; text; internal format)
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: A299991 A000977 A033992 * A308127 A091454 A175727

Adjacent sequences:  A214192 A214193 A214194 * A214196 A214197 A214198

KEYWORD

nonn

AUTHOR

Enrique Pérez Herrero, Jul 07 2012

STATUS

approved

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Last modified January 25 07:25 EST 2020. Contains 331241 sequences. (Running on oeis4.)