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Numbers n with prime factors less than 2*spf(n), where spf(m) is the smallest prime factor of m (A020639).
8

%I #14 Mar 04 2019 22:57:10

%S 1,2,3,4,5,6,7,8,9,11,12,13,15,16,17,18,19,23,24,25,27,29,31,32,35,36,

%T 37,41,43,45,47,48,49,53,54,59,61,64,67,71,72,73,75,77,79,81,83,89,91,

%U 96,97,101,103,107,108,109,113,121,125,127,128,131,135,137,139,143,144

%N Numbers n with prime factors less than 2*spf(n), where spf(m) is the smallest prime factor of m (A020639).

%C A081303(a(n)) < 0, A006530(a(n)) < A020639(a(n))*2.

%H Robert Israel, <a href="/A081306/b081306.txt">Table of n, a(n) for n = 1..10000</a>

%p filter:= proc(n) local F;

%p F:= numtheory:-factorset(n);

%p max(F) < 2*min(F);

%p end proc:

%p select(filter, [$1..200]); # _Robert Israel_, Mar 28 2018

%t Select[Range[200], Max[F = FactorInteger[#][[All, 1]]] < 2 Min[F]&] (* _Jean-François Alcover_, Mar 04 2019 *)

%Y Cf. A006530, A020639, A081303.

%Y Complement of A069900.

%Y Union of {1} and A069899. [_R. J. Mathar_, Sep 18 2008]

%K nonn

%O 1,2

%A _Reinhard Zumkeller_, Mar 17 2003