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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

Table of n, a(n) for n=1..21.

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

N. J. A. Sloane

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 May 21 14:51 EDT 2019. Contains 323443 sequences. (Running on oeis4.)