A067718 Numbers k such that sigma(2^k+1) == 0 (mod k).

1, 2, 6, 12, 24, 36, 42, 70, 126, 132, 144, 168, 210, 225, 252, 336, 344, 378, 385, 396, 462, 504, 528, 546, 560, 561, 576, 627, 630, 660, 672, 693, 714, 798, 896, 924, 930, 945, 960, 1001, 1008, 1012, 1032, 1050, 1116

Offset

1,2

Comments

1155 is also a term. - Husnain Raza, Oct 23 2024

Links

Table of n, a(n) for n=1..45.

Husnain Raza, Github link

Mathematica

Select[Range[150], Divisible[DivisorSigma[1, 2^# + 1], #] &] (* Amiram Eldar, Nov 28 2020 *)

Prog

(PARI) isok(n)=sigma(2^n+1)%n==0 \\ Klaus Brockhaus, Apr 13 2005

Crossrefs

Cf. A000051, A000203, A069061.

Sequence in context: A194096 A099993 A011778 * A210594 A307252 A306625

Adjacent sequences: A067715 A067716 A067717 * A067719 A067720 A067721

Keyword

nonn,hard,more

Author

Benoit Cloitre, Feb 05 2002

Extensions

a(13)-a(15) from Klaus Brockhaus, Apr 13 2005

a(16)-a(21) from Lars Blomberg, Jul 28 2017

a(22)-a(44) from Amiram Eldar, Nov 28 2020

a(45) from Husnain Raza, Sep 18 2024

Status

approved