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

1,2

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)

Mathematica

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

Prog

(PARI)
A065333(n) = ((3^valuation(n, 3)<<valuation(n, 2))==n); \\ From A065333
A354355(n) = A065333(sigma(n));
isA354356(n) = A354355(n);

Crossrefs

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

Cf. A005105, A046528, A354357 (subsequences).

Cf. also A122254.

Sequence in context: A302496 A117344 A117204 * A129127 A078135 A073328

Adjacent sequences: A354353 A354354 A354355 * A354357 A354358 A354359

Keyword

nonn

Author

Antti Karttunen, May 24 2022

Status

approved