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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 896701 is a term, found in 2010 (see link). - Jeppe Stig Nielsen, Jul 31 2020 REFERENCES N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS The Prime Pages, 8*3^896701 - 1. 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 October 28 06:26 EDT 2020. Contains 338048 sequences. (Running on oeis4.)