A349750 Odd numbers k such that sigma(k) == k (mod 3), where sigma is the sum of divisors function.

1, 15, 25, 33, 45, 51, 69, 87, 91, 99, 105, 121, 123, 133, 135, 141, 147, 153, 159, 165, 177, 195, 207, 213, 217, 231, 247, 249, 255, 259, 261, 267, 285, 289, 297, 301, 303, 315, 321, 339, 343, 345, 357, 369, 375, 393, 403, 405, 411, 423, 427, 429, 435, 441, 447, 459, 465, 469, 477, 481, 483, 495, 501, 507, 511, 519

Offset: 1

Author

Antti Karttunen, Nov 30 2021

Keywords

• nonn

Comments

Odd numbers k such that A010872(k) is equal to A074941(k).

Odd numbers k for which A001065(k) is a multiple of 3.

Links

• Index entries for sequences related to sigma(n)

Crossrefs

Cf. A000203, A001065, A010872, A074941, A349749, A349751.

Programs

Mathematica

Select[Range[1, 500, 2], Divisible[DivisorSigma[1, #] - #, 3] &] (* Amiram Eldar, Dec 01 2021 *)

PARI

isA349750(n) = ((n%2)&&0==(sigma(n)-n)%3);