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

1,1

Comments

Below 32 this sequence and A063989 are identical.

Links

Table of n, a(n) for n=1..67.

Mathematica

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

Prog

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

Crossrefs

Cf. A001222, A063989.

Sequence in context: A063806 A323521 A063989 * A282668 A117097 A077135

Adjacent sequences: A168642 A168643 A168644 * A168646 A168647 A168648

Keyword

nonn

Author

Juri-Stepan Gerasimov, Dec 01 2009

Status

approved