A276238 Numbers k such that 2^sigma(k) == -1 (mod k).

1, 5, 4097, 7361, 85073, 658529, 3999137, 16777217, 50281793, 68544541, 72281281, 78202273, 102931841, 128459137, 204786497, 244622261, 336392993, 613750913, 714155969, 785432401, 1008179297

Offset

1,2

Comments

Terms are 1, 5, 17*241, 17*433, 241*353, 17*38737, 353*11329, 97*257*673, ...

1074702941, 1250862433, 1440721697, 1568001217, 1713613525, 2140345601, 2540788609, 3275604737, 4755026593, 5468121409, 5762812001, 6115556525, 6449655809, 6653504801, 9817079873, 14262957473, 15268309153, 25080521857, 50944294561, ... are also terms. - Jinyuan Wang, Aug 26 2019

Links

Table of n, a(n) for n=1..21.

Example

5 is a term because 2^sigma(5) = 64 and 64 == -1 (mod 5).

Prog

(PARI) is(k) = Mod(2, k)^sigma(k) == -1;

Crossrefs

Cf. A000079, A000203.

Sequence in context: A073826 A159397 A024074 * A357125 A086896 A177503

Adjacent sequences: A276235 A276236 A276237 * A276239 A276240 A276241

Keyword

nonn,more

Author

Altug Alkan, Dec 12 2016

Extensions

a(13)-a(21) from Jinyuan Wang, Aug 26 2019

Status

approved