A354357 -id:A354357 - cp's OEIS frontend

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

Antti Karttunen, May 24 2022

nonn

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

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

Cf. A000203, A065333, A354355 (characteristic function).
Cf. A005105, A046528, A354357 (subsequences).
Cf. also A122254.

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

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

A354361 Numbers k such that A354203(sigma(A354202(k))) = 1.

Original entry on oeis.org

1, 2, 3, 6, 7, 13, 14, 19, 21, 23, 26, 38, 39, 41, 42, 43, 46, 57, 67, 69, 78, 82, 86, 91, 103, 107, 114, 123, 129, 133, 134, 138, 161, 179, 182, 201, 206, 214, 246, 247, 258, 266, 273, 287, 299, 301, 309, 321, 322, 358, 379, 399, 402, 419, 437, 469, 483, 494, 533, 537, 546, 559, 574, 598, 602, 618, 642, 643, 721

Offset: 1

Antti Karttunen, May 24 2022

nonn

Applying A354202 and sorting into ascending order gives A354357.

Positions of ones in A354206.

Cf. A000203, A354202, A354203, A354357.

isA354361(n) = (1==A354206(n)); \\ Uses the program given in A354206.

cp's OEIS Frontend

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

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