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

1,1

Comments

This sequence first differs from A053858 at 2310=2*3*5*7*11, which is in A053858 but not in this sequence.

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Formula

a(n) = 2 * A046388(n). - Amiram Eldar, Mar 03 2021

Example

30=2*3*5 and 42=2*3*7 are even, squarefree and have 3 prime factors.

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;

Mathematica

Select[2*Range[300], SquareFreeQ[#]&&PrimeNu[#]==3&] (* Harvey P. Dale, Feb 16 2018 *)

Prog

(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

Crossrefs

Cf. A046388, A053858.

Sequence in context: A007304 A160350 A053858 * A306217 A379029 A034683

Adjacent sequences: A075816 A075817 A075818 * A075820 A075821 A075822

Keyword

easy,nonn

Author

Jani Melik, Oct 13 2002

Extensions

Edited by Dean Hickerson, Oct 21 2002

Status

approved