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Odd numbers whose number of distinct prime factors is also odd.
4

%I #9 Feb 21 2014 03:13:10

%S 3,5,7,9,11,13,17,19,23,25,27,29,31,37,41,43,47,49,53,59,61,67,71,73,

%T 79,81,83,89,97,101,103,105,107,109,113,121,125,127,131,137,139,149,

%U 151,157,163,165,167,169,173,179,181,191,193,195,197,199,211,223,227,229

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

%C This will also contain all odd primes.

%H Vincenzo Librandi, <a href="/A098903/b098903.txt">Table of n, a(n) for n = 1..1000</a>

%e 25 is a member of sequence because 25 is odd and number of distinct prime factors of 25 i.e. 1 is also odd.

%t Select[Range[300],And@@OddQ[{#,PrimeNu[#]}]&] (* _Harvey P. Dale_, Feb 19 2014 *)

%Y Cf. A001221.

%K nonn,easy

%O 1,1

%A _Shyam Sunder Gupta_, Oct 14 2004