A081306 Numbers n with prime factors less than 2*spf(n), where spf(m) is the smallest prime factor of m (A020639).

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, 37, 41, 43, 45, 47, 48, 49, 53, 54, 59, 61, 64, 67, 71, 72, 73, 75, 77, 79, 81, 83, 89, 91, 96, 97, 101, 103, 107, 108, 109, 113, 121, 125, 127, 128, 131, 135, 137, 139, 143, 144

Offset: 1

Author

Reinhard Zumkeller, Mar 17 2003

Keywords

• nonn

Comments

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

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A006530, A020639, A081303.

Complement of A069900.

Union of {1} and A069899. [R. J. Mathar, Sep 18 2008]

Programs

Maple

filter:= proc(n) local F;
  F:= numtheory:-factorset(n);
  max(F) < 2*min(F);
end proc:
select(filter, [$1..200]); # Robert Israel, Mar 28 2018

Mathematica

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