A217072 Numbers k such that (k^19-1)/(k-1) is prime.

2, 10, 11, 12, 14, 19, 24, 40, 45, 46, 48, 65, 66, 67, 75, 85, 90, 103, 105, 117, 119, 137, 147, 164, 167, 179, 181, 205, 220, 235, 242, 253, 254, 263, 268, 277, 303, 315, 332, 337, 366, 369, 370, 389, 399, 404, 424, 431, 446, 449, 480, 481, 506, 509, 521, 523

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^19 - 1) div (n - 1))]; // Vincenzo Librandi, Sep 28 2012

Mathematica

Select[Range[2, 1000], PrimeQ[(#^19 - 1)/(# - 1)] &] (* T. D. Noe, Sep 26 2012 *)

PARI

is(n)=isprime((n^19-1)/(n-1)) \\ Charles R Greathouse IV, Feb 17 2017

Extensions

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