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A175863
Numbers k > 1 such that 2^(k-1) == (2*k + 1) (mod k^2).
0
7, 71, 379, 2659
OFFSET
1,1
COMMENTS
No further terms up to 5 million. - Harvey P. Dale, Mar 20 2016
The definition implies 2^(k-1) == 1 (mod k), so all terms are either primes or Sarrus numbers (A001567). There are no further prime terms below 10^12, and no further Sarrus terms below 2^64. - Lucas A. Brown, Feb 19 2024
MATHEMATICA
Select[Range[3000], PowerMod[2, #-1, #]==1&&PowerMod[2, #-1, #^2]-1==2*#&] (* Harvey P. Dale, Mar 20 2016 *)
CROSSREFS
Sequence in context: A137443 A362106 A107601 * A196742 A196900 A319963
KEYWORD
nonn,hard,more
AUTHOR
Alzhekeyev Ascar M, Sep 30 2010
STATUS
approved