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 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 (list; graph; refs; listen; history; text; internal format)
 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 EXTENSIONS More terms from Reinhard Zumkeller, Mar 10 2006 More terms from Klaus Brockhaus, Mar 20 2007 STATUS approved

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Last modified December 7 09:33 EST 2019. Contains 329843 sequences. (Running on oeis4.)