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%I #11 May 13 2013 01:49:41
%S 2,30,74,122,386,476,630
%N Numbers n such that 2*17^n - 1 is prime.
%C Is it true that a(n)= 0 or 2 (mod 6) and a(n)= 0 or 2 (mod 4)?
%C Yes. This can be proved mod 21. [_Charles R Greathouse IV_, Jul 31 2011]
%t Table[If[PrimeQ[2*17^m-1],m],{m,1,2000}]//Union
%o (PARI) forstep(n=2,1e4,[4,2],if(ispseudoprime(2*17^n-1),print1(n", "))) \\ _Charles R Greathouse IV_, Jul 31 2011
%K nonn
%O 1,1
%A _José María Grau Ribas_, Jul 17 2011
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