

A098905


Odd numbers whose number of distinct prime factors is positive and even.


4



15, 21, 33, 35, 39, 45, 51, 55, 57, 63, 65, 69, 75, 77, 85, 87, 91, 93, 95, 99, 111, 115, 117, 119, 123, 129, 133, 135, 141, 143, 145, 147, 153, 155, 159, 161, 171, 175, 177, 183, 185, 187, 189, 201, 203, 205, 207, 209, 213, 215, 217, 219, 221, 225, 235, 237
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OFFSET

1,1


LINKS

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


EXAMPLE

21 is a member of sequence because 21 is odd and number of distinct prime factors of 21, i.e., 2 is even.


MATHEMATICA

Select[Select[Range[2, 400], EvenQ[PrimeNu[#]] &], OddQ] (* G. C. Greubel, May 09 2017 *)
Select[Range[3, 250, 2], EvenQ[PrimeNu[#]]&] (* Harvey P. Dale, Jan 19 2020 *)


PROG

(PARI) isok(n) = (n>1) && (n%2) && !(omega(n) % 2); \\ Michel Marcus, Jan 20 2020
(MAGMA) [k:k in [3..250 by 2]IsEven(#PrimeDivisors(k))]; // Marius A. Burtea, Jan 20 2020


CROSSREFS

Cf. A001221.
Sequence in context: A275384 A185307 A061346 * A225375 A329229 A146166
Adjacent sequences: A098902 A098903 A098904 * A098906 A098907 A098908


KEYWORD

easy,nonn


AUTHOR

Shyam Sunder Gupta, Oct 14 2004


STATUS

approved



