A128465 -id:A128465 - cp's OEIS frontend

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

7, 71, 379, 2659

Offset: 1

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Alzhekeyev Ascar M, Sep 30 2010

nonn
hard
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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

Jan Feitsma, The pseudoprimes below 2^64.

Cf. A001567, A128465.

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

cp's OEIS Frontend

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

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