A046386 Products of four distinct primes.

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

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

Formula

Intersection of A014613 (product of 4 primes) and A033993 (divisible by 4 distinct primes). - M. F. Hasler, Mar 24 2022

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
(PARI) is(n) = omega(n)==4 && bigomega(n)==4 \\ Hugo Pfoertner, Dec 18 2018

Crossrefs

Cf. A001221 (omega), A001222 (bigomega), A014613 (bigomega(N) = 4) and A033993 (omega(N) = 4).

Cf. A006881, A007304, this, A046387, A067885 (products of 2, 3, 4, 5 and 6 distinct primes, respectively), A046402 (4 palindromic prime factors).

Sequence in context: A074159 A033993 A350373 * A229272 A046402 A258359

Adjacent sequences: A046383 A046384 A046385 * A046387 A046388 A046389

Keyword

nonn,easy

Author

Patrick De Geest, Jun 15 1998

Status

approved