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

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

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

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

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