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 A125871 Numbers n such that p=14n+1 is prime and cos(2pi/p) is an algebraic number of a 7-smooth degree, but not 5-smooth. 0
 2, 3, 5, 8, 9, 14, 15, 20, 24, 27, 30, 32, 35, 45, 48, 50, 54, 63, 72, 75, 98, 105, 144, 162, 180, 189, 192, 200, 224, 240, 252, 300, 320, 420, 450, 500, 504, 525, 540, 560, 588, 630, 750, 768, 864, 875, 900, 960, 980, 1029, 1080, 1134, 1215, 1280, 1323 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers n such that p=14n+1 is prime and the greatest prime divisor of p-1 is 7. LINKS MATHEMATICA Do[If[Take[FactorInteger[EulerPhi[14n+1]][[ -1]], 1]=={7} && PrimeQ[14n+1], Print[n]], {n, 1, 10000}] (*Artur Jasinski*) CROSSREFS Cf. A125866-A125878. Sequence in context: A270151 A009388 A190803 * A141399 A104737 A286495 Adjacent sequences:  A125868 A125869 A125870 * A125872 A125873 A125874 KEYWORD nonn AUTHOR Artur Jasinski, Dec 13 2006 EXTENSIONS Edited by Don Reble, Apr 24 2007 STATUS approved

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Last modified May 28 17:37 EDT 2020. Contains 334684 sequences. (Running on oeis4.)