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 A152008 Primes which are divisors of numbers of the form (2^phi(3^k) - 1)/3^k. 1

%I

%S 7,19,73,163,487,1459,2593,17497,39367,52489,71119,80191,87211,97687,

%T 135433,139483,209953,262657,379081

%N Primes which are divisors of numbers of the form (2^phi(3^k) - 1)/3^k.

%C The primes in this sequence have the property that with the exception of 7 they are congruent to 1 mod 18 and with the exception of 7, 19, 73 are congruent to 1 mod 54.

%t a = {}; Do[k = ((2^EulerPhi[3^(w + 1)] - 1)/3^(w + 1))/((2^EulerPhi[3^w] - 1)/3^w); Do[If[Mod[k, Prime[n]] == 0, AppendTo[a, Prime[n]]; Print[Prime[n]]], {n, PrimePi[2], PrimePi[379081]}], {w, 1, 20}]; Union[a] (*Artur Jasinski*)

%Y Cf. A008776, A152007.

%K hard,nonn

%O 1,1

%A _Artur Jasinski_, Nov 19 2008

%E Edited by _N. J. A. Sloane_, Nov 26 2008

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Last modified August 18 08:57 EDT 2019. Contains 326077 sequences. (Running on oeis4.)