A046339 Composite numbers with an odd number of prime factors (counted with multiplicity).

8, 12, 18, 20, 27, 28, 30, 32, 42, 44, 45, 48, 50, 52, 63, 66, 68, 70, 72, 75, 76, 78, 80, 92, 98, 99, 102, 105, 108, 110, 112, 114, 116, 117, 120, 124, 125, 128, 130, 138, 147, 148, 153, 154, 162, 164, 165, 168, 170, 171, 172, 174, 175, 176, 180, 182, 186, 188

Offset: 1

Author

Patrick De Geest, Jun 15 1998

Keywords

• nonn

Examples

			a(1)=8 as 8=2*2*2, that is 8 is a composite integer and having 3 (an odd number) prime factors.
		

Links

• John Cerkan, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A046340, A046341, A026424.

Programs

Mathematica

fQ[n_] := Block[{p = Plus @@ Last /@ FactorInteger@n}, OddQ[p] && p > 1]; Select[ Range@200, fQ[ # ] &] (* Robert G. Wilson v, Jan 04 2006 *)
Select[Range[200],CompositeQ[#]&&OddQ[PrimeOmega[#]]&] (* Harvey P. Dale, Oct 14 2019 *)

PARI

is(n)=!isprime(n) && bigomega(n)%2 \\ Charles R Greathouse IV, Sep 17 2015