A081765 Numbers k such that (k+2) divides 2^(k-1) - 1.

1, 7, 13, 19, 31, 37, 49, 55, 61, 67, 85, 91, 109, 121, 127, 139, 157, 175, 181, 193, 199, 211, 217, 235, 247, 265, 289, 301, 307, 313, 319, 325, 337, 379, 391, 397, 409, 415, 445, 451, 469, 487, 499, 517, 535, 541, 571, 577, 589, 595, 631, 667, 679, 685, 691

Offset: 1

Author

Benoit Cloitre, Apr 09 2003

Keywords

• easy
• nonn

Comments

Is a(n)/(n*log(n)*log(log(n))) bounded?

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000225.

Programs

Mathematica

Select[Range[1000], PowerMod[2, # - 1, # + 2] == 1 &] (* Amiram Eldar, Mar 30 2021 *)