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A005541 Numbers k such that 8*3^k - 1 is prime.
(Formerly M1200)
11

%I M1200

%S 0,1,2,4,10,17,50,170,184,194,209,641,1298,4034,5956,7154,9970,35956,

%T 42730,132004,190610

%N Numbers k such that 8*3^k - 1 is prime.

%C a(22) > 2*10^5. - _Robert Price_, Mar 16 2014

%C All terms are verified primes (i.e., not probable primes). - _Robert Price_, Mar 16 2014

%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

%H H. C. Williams and C. R. Zarnke, <a href="https://doi.org/10.1090/S0025-5718-1972-0314747-X">Some prime numbers of the forms 2*3^n+1 and 2*3^n-1</a>, Math. Comp., 26 (1972), 995-998.

%t lst={};Do[If[PrimeQ[8*3^n-1], AppendTo[lst, n]], {n, 13^3}];lst (* _Vladimir Joseph Stephan Orlovsky_, Sep 08 2008 *)

%o (PARI) is(n)=isprime(8*3^n-1) \\ _Charles R Greathouse IV_, Feb 17 2017

%Y Cf. A003307, A002235, A046865, A079906, A046866, A001771, A056725, A046867, A079907.

%K nonn,hard

%O 1,3

%A _N. J. A. Sloane_

%E More terms from Douglas Burke (dburke(AT)nevada.edu)

%E 0 prepended by _Vincenzo Librandi_, Sep 26 2012

%E a(18)-a(21) from _Robert Price_, Mar 16 2014

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Last modified November 15 06:30 EST 2019. Contains 329144 sequences. (Running on oeis4.)