A354356 Numbers k such that sigma(k) is 3-smooth (has no larger prime factors than 3).

1, 2, 3, 5, 6, 7, 10, 11, 14, 15, 17, 21, 22, 23, 30, 31, 33, 34, 35, 42, 46, 47, 51, 53, 55, 62, 66, 69, 70, 71, 77, 85, 93, 94, 102, 105, 106, 107, 110, 115, 119, 127, 138, 141, 142, 154, 155, 159, 161, 165, 170, 186, 187, 191, 210, 213, 214, 217, 230, 231, 235, 238, 253, 254, 255, 265, 282, 310, 318, 321, 322, 329

Offset: 1

Author

Antti Karttunen, May 24 2022

Keywords

• nonn

Comments

The prime terms in this sequence are in A005105. - Amiram Eldar, May 25 2022

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000
• Index entries for sequences related to sigma(n)

Crossrefs

Cf. A000203, A065333, A354355 (characteristic function).

Cf. A005105, A046528, A354357 (subsequences).

Cf. also A122254.

Programs

Mathematica

Select[Range[330], Max@ FactorInteger[DivisorSigma[1, #]][[All, 1]] <= 3 &] (* Michael De Vlieger, May 24 2022 *)

PARI

A065333(n) = ((3^valuation(n, 3)<A065333
A354355(n) = A065333(sigma(n));
isA354356(n) = A354355(n);