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

1,2

Links

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

Formula

A001221(a(n)) <= 2.

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

Example

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.

Mathematica

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

Prog

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

Crossrefs

Disjoint union of A000961 and A007774.

A003586 is a subsequence.

Cf. A001221.

Complement of A000977.

Sequence in context: A281873 A273888 A192218 * A083243 A004441 A004438

Adjacent sequences: A070912 A070913 A070914 * A070916 A070917 A070918

Keyword

nonn

Author

Reinhard Zumkeller, May 20 2002

Status

approved