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A046386
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Products of exactly four distinct primes.
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61
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210, 330, 390, 462, 510, 546, 570, 690, 714, 770, 798, 858, 870, 910, 930, 966, 1110, 1122, 1155, 1190, 1218, 1230, 1254, 1290, 1302, 1326, 1330, 1365, 1410, 1430, 1482, 1518, 1554, 1590, 1610, 1722, 1770, 1785, 1794, 1806, 1830, 1870, 1914, 1938, 1974
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OFFSET
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1,1
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COMMENTS
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A squarefree subsequence of A033993. Numbers like 420 = 2^2*3*5*7 with at least one prime exponent greater than 1 in the prime signature are excluded here. - R. J. Mathar, Apr 03 2011
Numbers such that omega(n) = bigomega(n) = 4. - Michel Marcus, Dec 15 2015
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LINKS
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FORMULA
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EXAMPLE
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210 = 2*3*5*7;
330 = 2*3*5*11;
390 = 2*3*5*13;
462 = 2*3*7*11.
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MATHEMATICA
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fQ[n_] := Last /@ FactorInteger[n] == {1, 1, 1, 1}; Select[ Range[2000], fQ[ # ] &] (* Robert G. Wilson v, Aug 04 2005 *)
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PROG
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(PARI) is(n) = omega(n)==4 && bigomega(n)==4 \\ Hugo Pfoertner, Dec 18 2018
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CROSSREFS
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Cf. A046402 (4 palindromic prime factors).
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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