A125876 Prime numbers n such that cos(2pi/n) is an algebraic number of a 13-smooth degree, but not 11-smooth.

53, 79, 131, 157, 313, 521, 547, 677, 859, 911, 937, 1093, 1171, 1249, 1301, 1873, 1951, 2003, 2029, 2081, 2341, 2549, 2731, 2861, 3121, 3251, 3329, 3433, 3511, 3719, 3823, 4057, 4733, 4993, 5851, 6007, 6553, 6761, 7151, 7489, 7723, 8009

Offset: 1

Author

Artur Jasinski, Dec 13 2006

Keywords

• nonn

Crossrefs

Cf. A125866-A125878.

Programs

Mathematica

Do[If[Take[FactorInteger[EulerPhi[2n+1]][[ -1]],1]=={13} && PrimeQ[2n+1],Print[2n+1]],{n,1,10000}] (*Artur Jasinski*)

Extensions

Edited by Don Reble, Apr 24 2007