

A171241


Numbers n such that (number of prime divisors of n <= 3) = 3.


1



8, 12, 18, 27, 40, 56, 60, 84, 88, 90, 104, 126, 132, 135, 136, 152, 156, 184, 189, 198, 200, 204, 228, 232, 234, 248, 276, 280, 296, 297, 300, 306, 328, 342, 344, 348, 351, 372, 376, 392, 414, 420, 424, 440, 444, 450, 459, 472, 488, 492, 513, 516, 520, 522
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OFFSET

1,1


COMMENTS

Numbers of the form k*m where k is in {8, 12, 18, 27} and gcd(m, 6) = 1.  David A. Corneth, Aug 31 2019


LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000


FORMULA

A169611(a(n)) = 3.


MATHEMATICA

aQ[n_] := Plus @@ Last /@ Select[FactorInteger@n, 1 < #[[1]] < 4 &] == 3; Select[Range[522], aQ] (* Amiram Eldar, Aug 31 2019 after Robert G. Wilson v at A169611 *)


PROG

(PARI) is(n) = bigomega(gcd(n, 1296)) == 3 \\ David A. Corneth, Aug 31 2019


CROSSREFS

Cf. A007310, A169611, A171126.
Sequence in context: A028393 A066681 A276403 * A120137 A274951 A033477
Adjacent sequences: A171238 A171239 A171240 * A171242 A171243 A171244


KEYWORD

nonn,easy


AUTHOR

JuriStepan Gerasimov, Dec 05 2009


EXTENSIONS

Corrected (200, 232, 280 inserted) and extended by R. J. Mathar, Jun 04 2010
Name corrected by Amiram Eldar, Aug 31 2019


STATUS

approved



