A145784 Numbers with property that the number of prime factors is a multiple of 3.

1, 8, 12, 18, 20, 27, 28, 30, 42, 44, 45, 50, 52, 63, 64, 66, 68, 70, 75, 76, 78, 92, 96, 98, 99, 102, 105, 110, 114, 116, 117, 124, 125, 130, 138, 144, 147, 148, 153, 154, 160, 164, 165, 170, 171, 172, 174, 175, 182, 186, 188, 190, 195, 207, 212, 216, 222

Offset

1,2

Comments

A multiplicative semigroup: if m and n are in the sequence, then so is m*n. - Antti Karttunen, Jul 02 2024

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Formula

A010872(A001222(a(n))) = 0.

Mathematica

Join[{1}, Select[Range[2, 230], Mod[Total[Transpose[FactorInteger[#]][[2]]], 3] == 0 &]] (* T. D. Noe, May 21 2012 *)

Prog

(Haskell)
a145784 n = a145784_list !! (n-1)
a145784_list = filter ((== 0) . a010872 . a001222) [1..]
-- Reinhard Zumkeller, May 26 2012

Crossrefs

Cf. A001222, A010872, A373975 (characteristic function).

Subsequences: A000578, A014612, A046316, A121307, A373589, A373590, A373597, A373837.

Cf. also A028260, A214195, A297845.

Sequence in context: A051144 A067537 A046339 * A358763 A014612 A226527

Adjacent sequences: A145781 A145782 A145783 * A145785 A145786 A145787

Keyword

nonn

Author

Reinhard Zumkeller, Oct 19 2008

Status

approved