A217075 Numbers k such that (k^31-1)/(k-1) is prime.

2, 14, 19, 31, 44, 53, 71, 82, 117, 127, 131, 145, 177, 197, 203, 241, 258, 261, 276, 283, 293, 320, 325, 379, 387, 388, 406, 413, 461, 462, 470, 486, 491, 534, 549, 569, 582, 612, 618, 639, 696, 706, 723, 746, 765, 767, 774, 796, 802, 877, 878, 903, 923, 981

Offset: 1

Author

Tim Johannes Ohrtmann, Sep 26 2012

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A002384, A049409, A100330, A162862, A217070-A217089.

Programs

Magma

[n: n in [2..1000] |IsPrime((n^31 - 1) div (n - 1))]; // Vincenzo Librandi, Sep 28 2012

Mathematica

Select[Range[2, 1000], PrimeQ[(#^31 - 1)/(# - 1)] &] (* T. D. Noe, Sep 26 2012 *)

PARI

is(n)=isprime((n^31-1)/(n-1)) \\ Charles R Greathouse IV, Feb 17 2017

Extensions

More terms from T. D. Noe, Sep 26 2012