

A046386


Products of four distinct primes.


30



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

1,1


COMMENTS

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


LINKS

T. D. Noe, Table of n, a(n) for n = 1..10000


EXAMPLE

210 = 2*3*5*7. 330 = 2*3*5*11. 390 = 2*3*5*13. 462 = 2*3*7*11.


MATHEMATICA

fQ[n_] := Last /@ FactorInteger[n] == {1, 1, 1, 1}; Select[ Range[2000], fQ[ # ] &] (* Robert G. Wilson v, Aug 04 2005 *)


PROG

(PARI) is(n)=factor(n)[, 2]==[1, 1, 1, 1]~ \\ Charles R Greathouse IV, Sep 17 2015


CROSSREFS

Cf. A046387, A067885 (product of 5 and 6 distinct primes, resp.)
Cf. A006881, A007304, A014613, A046402.
Sequence in context: A127424 A074159 A033993 * A229272 A046402 A258359
Adjacent sequences: A046383 A046384 A046385 * A046387 A046388 A046389


KEYWORD

nonn,easy


AUTHOR

Patrick De Geest, Jun 15 1998


STATUS

approved



