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

1,1

Links

Table of n, a(n) for n=1..42.

Mathematica

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

Crossrefs

Cf. A125866-A125878.

Sequence in context: A125875 A059245 A268753 * A136065 A354915 A234102

Adjacent sequences: A125873 A125874 A125875 * A125877 A125878 A125879

Keyword

nonn

Author

Artur Jasinski, Dec 13 2006

Extensions

Edited by Don Reble, Apr 24 2007

Status

approved