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 A033993 Numbers that are divisible by exactly four different primes. 22
 210, 330, 390, 420, 462, 510, 546, 570, 630, 660, 690, 714, 770, 780, 798, 840, 858, 870, 910, 924, 930, 966, 990, 1020, 1050, 1092, 1110, 1122, 1140, 1155, 1170, 1190, 1218, 1230, 1254, 1260, 1290, 1302, 1320, 1326, 1330, 1365, 1380, 1386, 1410, 1428 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For a(n) < 30030 = 2 * 3 * 5 * 7 * 11 * 13 this is identical to "numbers with a semiprime number of distinct prime factors." - Jonathan Vos Post, Sep 21 2005 LINKS T. D. Noe, Table of n, a(n) for n = 1..1000 FORMULA a(n) has exactly 4 distinct prime factors. omega(a(n)) = A001221(a(n)) = 4. - Jonathan Vos Post, Sep 21 2005 EXAMPLE The 4th primorial is the first term of this sequence: A002110(4) = 210. MATHEMATICA Select[Range[1500], Length[FactorInteger[#]] == 4 &] (* Vladimir Joseph Stephan Orlovsky, Apr 22 2010 *) PROG (PARI) is(n)=omega(n)==4 \\ Charles R Greathouse IV, Sep 17 2015 CROSSREFS Cf. A000977, A007774, A000961, A002110, A033992, A051270, A001221. Sequence in context: A119427 A127424 A074159 * A046386 A229272 A046402 Adjacent sequences:  A033990 A033991 A033992 * A033994 A033995 A033996 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified October 22 17:34 EDT 2019. Contains 328319 sequences. (Running on oeis4.)