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A125877
Numbers n such that p=26n+1 is prime and cos(2pi/p) is an algebraic number of a 13-smooth degree, but not 11-smooth.
2
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
1,1
COMMENTS
Numbers n such that p=26n+1 is prime and the greatest prime divisor of p-1 is 13.
LINKS
MATHEMATICA
Do[If[Take[FactorInteger[EulerPhi[26n+1]][[ -1]], 1]=={13} && PrimeQ[26n+1], Print[n]], {n, 1, 10000}] (*Artur Jasinski*)
Select[Range[600], PrimeQ[26#+1]&&FactorInteger[26#][[-1, 1]]==13&] (* Harvey P. Dale, Jun 01 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Artur Jasinski, Dec 13 2006
EXTENSIONS
Edited by Don Reble, Apr 24 2007
STATUS
approved