A004612 Numbers that are divisible only by primes congruent to 2 mod 3.

1, 2, 4, 5, 8, 10, 11, 16, 17, 20, 22, 23, 25, 29, 32, 34, 40, 41, 44, 46, 47, 50, 53, 55, 58, 59, 64, 68, 71, 80, 82, 83, 85, 88, 89, 92, 94, 100, 101, 106, 107, 110, 113, 115, 116, 118, 121, 125, 128, 131, 136, 137

Offset

1,2

Comments

Square roots of numbers n such that n-th coefficient of eta(x)^3/eta(x^3)=-1, where eta(x) is given by A010815. - Benoit Cloitre, Oct 06 2005

Apparently the complement to A135412. - R. J. Mathar, Aug 21 2016

Links

T. D. Noe, Table of n, a(n) for n = 1..10000

Example

2=2, 4=2^2, 5=5, 8=2^3, 10=2*5, 11=11, 16=2^4, 17=17, 20=2^2*5, 22 = 2*11, 23=23, 25=5^2, 29=29... (products of powers of elements of A003627). - R. J. Mathar, Jan 22 2021

Mathematica

ok[1]=True; ok[n_]:=And@@(Mod[#, 3]==2&)/@FactorInteger[n][[All, 1]]; Select[Range[200], ok] (* Vincenzo Librandi, Aug 21 2012 *)

Prog

(Magma) [n: n in [1..300] | forall{d: d in PrimeDivisors(n) | d mod 3 eq 2}]; // Vincenzo Librandi, Aug 21 2012

Crossrefs

Cf. A004611, A003627.

Sequence in context: A102798 A247886 A244991 * A066208 A357981 A169743

Adjacent sequences: A004609 A004610 A004611 * A004613 A004614 A004615

Keyword

nonn

Author

N. J. A. Sloane

Status

approved