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%I #5 Oct 19 2017 03:15:05
%S 23,67,89,199,331,353,397,463,617,661,727,881,991,1321,1409,1453,1783,
%T 2113,2179,2311,2377,2663,2971,3169,3301,3389,3631,3697,3851,4159,
%U 4357,4621,4951,5281,5347,5501,6337,6469,7129,7393,7547,8317,8713
%N Prime numbers n such that cos(2pi/n) is an algebraic number of an 11-smooth degree, but not 7-smooth.
%t Do[If[Take[FactorInteger[EulerPhi[2n+1]][[ -1]],1]=={11} && PrimeQ[2n+1],Print[2n+1]],{n,1,10000}] (*Artur Jasinski*)
%Y Cf. A125866-A125878.
%K nonn
%O 1,1
%A _Artur Jasinski_, Dec 13 2006
%E Edited by _Don Reble_, Apr 24 2007
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