A175863 Numbers k > 1 such that 2^(k-1) == (2*k + 1) (mod k^2).

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

Links

Table of n, a(n) for n=1..4.

Jan Feitsma, The pseudoprimes below 2^64.

Mathematica

Select[Range[3000], PowerMod[2, #-1, #]==1&&PowerMod[2, #-1, #^2]-1==2*#&] (* Harvey P. Dale, Mar 20 2016 *)

Crossrefs

Cf. A001567, A128465.

Sequence in context: A137443 A362106 A107601 * A196742 A196900 A319963

Adjacent sequences: A175860 A175861 A175862 * A175864 A175865 A175866

Keyword

nonn,hard,more

Author

Alzhekeyev Ascar M, Sep 30 2010

Status

approved