A374135 Nonmultiples of 3 whose sum of divisors is also a nonmultiple of 3.

1, 4, 7, 13, 16, 19, 25, 28, 31, 37, 43, 52, 61, 64, 67, 73, 76, 79, 91, 97, 100, 103, 109, 112, 121, 124, 127, 133, 139, 148, 151, 157, 163, 172, 175, 181, 193, 199, 208, 211, 217, 223, 229, 241, 244, 247, 256, 259, 268, 271, 277, 283, 289, 292, 301, 304, 307, 313, 316, 325, 331, 337, 343, 349, 364, 367, 373, 379

Offset

1,2

Comments

Numbers k such that Ramanujan tau(k), A000594(k), is not a multiple of 3.

Not a multiplicative semigroup. For example, although 7 is included, 49 = 7*7 is not.

Links

Antti Karttunen, Table of n, a(n) for n = 1..20000

Index entries for sequences related to sigma(n)

Mathematica

Select[Range[380], Mod[#, 3]!=0&&Mod[DivisorSigma[1, #], 3]!=0 &] (* Stefano Spezia, Jul 03 2024 *)

Prog

(PARI)
A070563(n) = ((n%3) && (sigma(n)%3));
isA374135 = A070563;

Crossrefs

Intersection of A001651 and A329963.

Cf. A000203, A000594, A070563 (characteristic function).

Sequence in context: A191201 A084089 A202822 * A137827 A045090 A213382

Adjacent sequences: A374132 A374133 A374134 * A374136 A374137 A374138

Keyword

nonn

Author

Antti Karttunen, Jul 03 2024

Status

approved