A070915 Numbers having at most two distinct prime factors.

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 61, 62, 63, 64, 65, 67, 68, 69, 71

Offset: 1

Author

Reinhard Zumkeller, May 20 2002

Keywords

• nonn

Examples

			88 and 77 are terms, as 88=11*2^3 and 77=11*7, but 66 is not a term, as 66 = 11*3*2.
		

Links

• G. C. Greubel, Table of n, a(n) for n = 1..10000

Crossrefs

Disjoint union of A000961 and A007774.

A003586 is a subsequence.

Cf. A001221.

Complement of A000977.

Programs

Mathematica

Select[Range[80],PrimeNu[#]<3&] (* Harvey P. Dale, Sep 19 2012 *)

PARI

is(n)=omega(n)<3 \\ Charles R Greathouse IV, Oct 16 2015

Formula

A001221(a(n)) <= 2.

a(n) ~ n log n/log log n. - Charles R Greathouse IV, Oct 16 2015