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

1,1

Links

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

Example

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

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 *)

Prog

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

Crossrefs

Cf. A046340, A046341, A026424.

Sequence in context: A340681 A051144 A067537 * A145784 A358763 A014612

Adjacent sequences: A046336 A046337 A046338 * A046340 A046341 A046342

Keyword

nonn

Author

Patrick De Geest, Jun 15 1998

Status

approved