A075819 Even squarefree numbers with exactly 3 prime factors.
30, 42, 66, 70, 78, 102, 110, 114, 130, 138, 154, 170, 174, 182, 186, 190, 222, 230, 238, 246, 258, 266, 282, 286, 290, 310, 318, 322, 354, 366, 370, 374, 402, 406, 410, 418, 426, 430, 434, 438, 442, 470, 474, 494, 498, 506, 518, 530, 534, 574, 582, 590
Offset: 1
Examples
30=2*3*5 and 42=2*3*7 are even, squarefree and have 3 prime factors.
Links
- Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
Programs
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Maple
ts_3_sod := proc(n); if (numtheory[bigomega](n)=3 and numtheory[mobius](n)=-1 and type(n,even)='true') then RETURN(n); fi end: a3sod := [seq(ts_3_sod(i), i=1..2500)]: a3sod;
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Mathematica
Select[2*Range[300],SquareFreeQ[#]&&PrimeNu[#]==3&] (* Harvey P. Dale, Feb 16 2018 *)
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PARI
list(lim)=my(v=List()); forprime(p=5, lim\6, forprime(q=3, min(lim\(2*p),p-2), listput(v, 2*p*q))); Set(v) \\ Charles R Greathouse IV, Aug 29 2017
Formula
a(n) = 2 * A046388(n). - Amiram Eldar, Mar 03 2021
Extensions
Edited by Dean Hickerson, Oct 21 2002
Comments