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A125867
Numbers k such that p=6k+1 is prime and cos(2*Pi/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
OFFSET
1,2
COMMENTS
Numbers k such that p=6k+1 is prime and the greatest prime divisor of p-1 is 3.
MATHEMATICA
Do[If[Take[FactorInteger[EulerPhi[6n+1]][[ -1]], 1]=={3} && PrimeQ[6n+1], Print[n]], {n, 1, 100000}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Artur Jasinski, Dec 13 2006
EXTENSIONS
Edited by Don Reble, Apr 24 2007
STATUS
approved