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A067718
Numbers k such that sigma(2^k+1) == 0 (mod k).
1
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
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
KEYWORD
nonn,hard,more,changed
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