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A354356
Numbers k such that sigma(k) is 3-smooth (has no larger prime factors than 3).
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
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
KEYWORD
nonn
AUTHOR
Antti Karttunen, May 24 2022
STATUS
approved