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A354357
Numbers k, not divisible by 2 or 3, such that sigma(k) is 3-smooth (has no larger prime factors than 3).
3
1, 5, 7, 11, 17, 23, 31, 35, 47, 53, 55, 71, 77, 85, 107, 115, 119, 127, 155, 161, 187, 191, 217, 235, 253, 265, 329, 341, 355, 371, 383, 385, 391, 431, 497, 517, 527, 535, 583, 595, 635, 647, 713, 749, 781, 799, 805, 863, 889, 901, 935, 955, 971, 1081, 1085, 1151, 1177, 1207, 1219, 1265, 1309, 1337, 1397, 1457, 1633
OFFSET
1,2
LINKS
MATHEMATICA
Select[Flatten @ Outer[Plus, 6 * Range[0, 300], {1, 5}], Max @ FactorInteger[DivisorSigma[1, #]][[;; , 1]] <= 3 &] (* Amiram Eldar, May 25 2022 *)
Select[Range[1, 1701, 2], Mod[#, 3]!=0&&Max[FactorInteger[DivisorSigma[1, #]][[;; , 1]]]<4&] (* Harvey P. Dale, Dec 17 2023 *)
PROG
(PARI)
A065333(n) = ((3^valuation(n, 3)<<valuation(n, 2))==n); \\ From A065333
A354355(n) = A065333(sigma(n));
isA354357(n) = ((n%2)&&(n%3)&&A354355(n));
CROSSREFS
Intersection of A007310 and A354356.
Sequence A354202(A354361(n)), n>=1, sorted into ascending order.
Sequence in context: A300097 A166574 A163846 * A156104 A191080 A293200
KEYWORD
nonn
AUTHOR
Antti Karttunen, May 24 2022
STATUS
approved