A074628 Numbers k such that sigma(k) == 2 mod 6.

7, 13, 19, 21, 28, 31, 37, 39, 43, 52, 57, 61, 63, 67, 73, 76, 79, 84, 93, 97, 103, 109, 111, 112, 117, 124, 127, 129, 139, 148, 151, 156, 157, 163, 171, 172, 175, 181, 183, 189, 193, 199, 201, 208, 211, 219, 223, 228, 229, 237, 241, 244, 252

Offset: 1

Author

Labos Elemer, Aug 26 2002

Keywords

• easy
• nonn

Examples

			For k=39: sigma(39) = 1+3+13+39 = 56 = 6*9 + 2.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000203, A072862, A074384, A074627, A074628, A074629, A074630.

Programs

Mathematica

Select[Range[300],Mod[DivisorSigma[1,#],6]==2&] (* Harvey P. Dale, Nov 14 2014 *)

PARI

isok(n) = ((sigma(n) % 6) == 2); \\ Michel Marcus, Dec 19 2013

Formula

A000203(n) mod 6 = 2.

{n: A084301(n) = 2}. - R. J. Mathar, May 19 2020