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 A005541 Numbers k such that 8*3^k - 1 is prime. (Formerly M1200) 11
 0, 1, 2, 4, 10, 17, 50, 170, 184, 194, 209, 641, 1298, 4034, 5956, 7154, 9970, 35956, 42730, 132004, 190610 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS a(22) > 2*10^5. - Robert Price, Mar 16 2014 All terms are verified primes (i.e., not probable primes). - Robert Price, Mar 16 2014 REFERENCES N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS H. C. Williams and C. R. Zarnke, Some prime numbers of the forms 2*3^n+1 and 2*3^n-1, Math. Comp., 26 (1972), 995-998. MATHEMATICA lst={}; Do[If[PrimeQ[8*3^n-1], AppendTo[lst, n]], {n, 13^3}]; lst (* Vladimir Joseph Stephan Orlovsky, Sep 08 2008 *) PROG (PARI) is(n)=isprime(8*3^n-1) \\ Charles R Greathouse IV, Feb 17 2017 CROSSREFS Cf. A003307, A002235, A046865, A079906, A046866, A001771, A056725, A046867, A079907. Sequence in context: A285939 A034455 A057491 * A045955 A182248 A093695 Adjacent sequences:  A005538 A005539 A005540 * A005542 A005543 A005544 KEYWORD nonn,hard AUTHOR EXTENSIONS More terms from Douglas Burke (dburke(AT)nevada.edu) 0 prepended by Vincenzo Librandi, Sep 26 2012 a(18)-a(21) from Robert Price, Mar 16 2014 STATUS approved

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Last modified January 25 03:49 EST 2020. Contains 331241 sequences. (Running on oeis4.)