A098904 - OEIS

A098904

Even numbers whose number of distinct prime factors is odd.

2, 4, 8, 16, 30, 32, 42, 60, 64, 66, 70, 78, 84, 90, 102, 110, 114, 120, 126, 128, 130, 132, 138, 140, 150, 154, 156, 168, 170, 174, 180, 182, 186, 190, 198, 204, 220, 222, 228, 230, 234, 238, 240, 246, 252, 256, 258, 260, 264, 266, 270, 276, 280, 282, 286, 290

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OFFSET

1,1

LINKS

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

EXAMPLE

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

MATHEMATICA

Select[Select[Range[500], OddQ[PrimeNu[#]] &], EvenQ] (* G. C. Greubel, May 21 2017 *)

Select[2*Range[150], OddQ[PrimeNu[#]]&] (* Harvey P. Dale, Aug 15 2020 *)

PROG

(PARI) is(k) = !(k % 2) && omega(k) % 2; \\ Amiram Eldar, Sep 18 2024