1,1

G. C. Greubel, Table of n, a(n) for n = 1..1000

a(n) ~ A033992(n) ~ 2n log n / (log log n)^2. - Charles R Greathouse IV, Jul 28 2016

2310=2*3*5*7*11 has 5 prime factors, hence it is not here, but it is part of A064040.

Select[Range[106], MemberQ[{2, 3}, PrimeNu[#]]&] (* Jayanta Basu, Jun 04 2013 *)

(PARI) is(n)=my(o=omega(n)); o==2 || o==3 \\ Charles R Greathouse IV, Jul 28 2016

Sequence in context: A325265 A105642 A064040 * A024619 A335080 A323304

Adjacent sequences: A168635 A168636 A168637 * A168639 A168640 A168641

nonn

Juri-Stepan Gerasimov, Dec 01 2009

approved