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

Author

N. J. A. Sloane

Keywords

• nonn

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

Examples

			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
		

Links

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

Crossrefs

Cf. A004611, A003627.

Programs

Magma

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

Mathematica

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