A125877 Numbers k such that p=26*k+1 is prime and cos(2*Pi/p) is an algebraic number of a 13-smooth degree, but not 11-smooth.

2, 3, 5, 6, 12, 20, 21, 26, 33, 35, 36, 42, 45, 48, 50, 72, 75, 77, 78, 80, 90, 98, 105, 110, 120, 125, 128, 132, 135, 143, 147, 156, 182, 192, 225, 231, 252, 260, 275, 288, 297, 308, 315, 330, 336, 351, 363, 378, 390, 392, 405, 441, 450, 455, 486, 500, 507, 512

Offset: 1

Author

Artur Jasinski, Dec 13 2006

Keywords

• nonn

Comments

Numbers k such that p=26*k+1 is prime and the greatest prime divisor of p-1 is 13.

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A125866-A125878.

Programs

Mathematica

Do[If[Take[FactorInteger[EulerPhi[26n+1]][[ -1]],1]=={13} && PrimeQ[26n+1],Print[n]],{n,1,10000}]
(* or *)
Select[Range[600],PrimeQ[26#+1]&&FactorInteger[26#][[-1,1]]==13&] (* Harvey P. Dale, Jun 01 2019 *)

Extensions

Edited by Don Reble, Apr 24 2007