A098904 - OEIS

%I #14 Sep 18 2024 08:43:48

%S 2,4,8,16,30,32,42,60,64,66,70,78,84,90,102,110,114,120,126,128,130,

%T 132,138,140,150,154,156,168,170,174,180,182,186,190,198,204,220,222,

%U 228,230,234,238,240,246,252,256,258,260,264,266,270,276,280,282,286,290

%N Even numbers whose number of distinct prime factors is odd.

%H G. C. Greubel, <a href="/A098904/b098904.txt">Table of n, a(n) for n = 1..1000</a>

%e 30 is a member of sequence because 30 is even and number of distinct prime factors of 30, i.e., 3 is odd.

%t Select[Select[Range[500], OddQ[PrimeNu[#]] &], EvenQ] (* _G. C. Greubel_, May 21 2017 *)

%t Select[2*Range[150],OddQ[PrimeNu[#]]&] (* _Harvey P. Dale_, Aug 15 2020 *)

%o (PARI) is(k) = !(k % 2) && omega(k) % 2; \\ _Amiram Eldar_, Sep 18 2024

%Y Cf. A001221, A098902, A098903, A098905.

%K easy,nonn,changed

%O 1,1

%A _Shyam Sunder Gupta_, Oct 14 2004