A349751 Odd numbers k such that sigma(k) == -k (mod 3), where sigma is the sum of divisors function.

7, 13, 15, 19, 31, 33, 37, 43, 45, 51, 61, 67, 69, 73, 79, 87, 97, 99, 103, 105, 109, 123, 127, 135, 139, 141, 147, 151, 153, 157, 159, 163, 165, 175, 177, 181, 193, 195, 199, 207, 211, 213, 223, 229, 231, 241, 249, 255, 261, 267, 271, 277, 283, 285, 297, 303, 307, 313, 315, 321, 325, 331, 337, 339, 345, 349, 357

Offset

1,1

Comments

Odd numbers k for which A155085(k) is a multiple of 3.

Links

Table of n, a(n) for n=1..67.

Index entries for sequences where odd perfect numbers must occur, if they exist at all

Index entries for sequences related to sigma(n)

Example

7 is present as 7 mod 3 = +1, while sigma(7) = 8, and 8 mod 3 = 2, i.e., -1.
45 is present as 45 mod 3 = 0, while sigma(45) = 78, and 78 mod 3 = 0 as well.

Mathematica

Select[Range[1, 360, 2], Divisible[DivisorSigma[1, #] + #, 3] &] (* Amiram Eldar, Dec 01 2021 *)

Prog

(PARI) isA349751(n) = ((n%2)&&0==(sigma(n)+n)%3);

Crossrefs

Cf. A000203, A010872, A074941, A155085, A349750.

Cf. A349752 (intersection with A349749).

Sequence in context: A349749 A076196 A330431 * A349752 A167782 A326380

Adjacent sequences: A349748 A349749 A349750 * A349752 A349753 A349754

Keyword

nonn

Author

Antti Karttunen, Nov 30 2021

Status

approved