A168645 Numbers with 2 or 3 prime divisors (counted with multiplicity).

4, 6, 8, 9, 10, 12, 14, 15, 18, 20, 21, 22, 25, 26, 27, 28, 30, 33, 34, 35, 38, 39, 42, 44, 45, 46, 49, 50, 51, 52, 55, 57, 58, 62, 63, 65, 66, 68, 69, 70, 74, 75, 76, 77, 78, 82, 85, 86, 87, 91, 92, 93, 94, 95, 98, 99, 102, 105, 106, 110, 111, 114, 115, 116, 117, 118, 119

Offset: 1

Author

Juri-Stepan Gerasimov, Dec 01 2009

Keywords

• nonn

Comments

Below 32 this sequence and A063989 are identical.

Crossrefs

Cf. A001222, A063989.

Programs

Mathematica

Select[Range[150],MemberQ[{2,3},Total[Transpose[ FactorInteger[#]] [[2]]]]&]  (* Harvey P. Dale, Mar 28 2011 *)

PARI

is(n)=my(t=bigomega(n)); t==2 || t==3 \\ Charles R Greathouse IV, Jun 19 2016