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 A125867 Numbers n such that p=6n+1 is prime and cos(2pi/p) is an algebraic number of a 3-smooth degree, but not 2-smooth. 3
 1, 2, 3, 6, 12, 16, 18, 27, 32, 72, 81, 96, 128, 192, 216, 243, 432, 486, 576, 648, 1728, 2048, 2916, 3072, 6561, 8748, 23328, 24576, 34992, 55296, 78732, 104976, 124416, 131072, 139968, 165888, 196608, 248832, 294912, 331776, 442368, 839808 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that p=6n+1 is prime and the greatest prime divisor of p-1 is 3. LINKS MATHEMATICA Do[If[Take[FactorInteger[EulerPhi[6n+1]][[ -1]], 1]=={3} && PrimeQ[6n+1], Print[n]], {n, 1, 100000}] CROSSREFS Cf. A024899, A058383, A125866-A125878. Sequence in context: A124485 A200175 A286906 * A032727 A323392 A174801 Adjacent sequences:  A125864 A125865 A125866 * A125868 A125869 A125870 KEYWORD nonn AUTHOR Artur Jasinski, Dec 13 2006 EXTENSIONS Edited by Don Reble, Apr 24 2007 STATUS approved

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Last modified January 19 11:16 EST 2022. Contains 350465 sequences. (Running on oeis4.)