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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
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
KEYWORD
nonn,hard
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