

A037144


Numbers with at most 3 prime factors (counted with multiplicity).


13



1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 17, 18, 19, 20, 21, 22, 23, 25, 26, 27, 28, 29, 30, 31, 33, 34, 35, 37, 38, 39, 41, 42, 43, 44, 45, 46, 47, 49, 50, 51, 52, 53, 55, 57, 58, 59, 61, 62, 63, 65, 66, 67, 68, 69, 70, 71, 73, 74, 75, 76, 77, 78, 79, 82, 83, 85, 86
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OFFSET

1,2


COMMENTS

Complement of A033987: A001222(a(n))<=3; A117358(a(n))=1.  Reinhard Zumkeller, Mar 10 2006
Also numbers such that exist permutations of all proper divisors only with coprime adjacent elements: A178254(a(n))>0.  Reinhard Zumkeller, May 24 2010


LINKS

Klaus Brockhaus, Table of n, a(n) for n = 1..10000


FORMULA

a(n) ~ 2n log n/(log log n)^2.  Charles R Greathouse IV, Sep 14 2015


MATHEMATICA

Select[Range[100], PrimeOmega[#]<4&] (* Harvey P. Dale, Oct 15 2015 *)


PROG

(MAGMA) [ n: n in [1..86]  n eq 1 or &+[ t[2]: t in Factorization(n) ] le 3 ]; /* Klaus Brockhaus, Mar 20 2007 */
(PARI) is(n)=bigomega(n)<4 \\ Charles R Greathouse IV, Sep 14 2015


CROSSREFS

A037143 is a subsequence.
Cf. A033987, A001222, A117358, A128644.
Sequence in context: A028261 A119675 A253781 * A121684 A191853 A123093
Adjacent sequences: A037141 A037142 A037143 * A037145 A037146 A037147


KEYWORD

nonn


AUTHOR

N. J. A. Sloane.


EXTENSIONS

More terms from Reinhard Zumkeller, Mar 10 2006
More terms from Klaus Brockhaus, Mar 20 2007


STATUS

approved



