OFFSET
1,2
COMMENTS
a(8) > 30000. - Giovanni Resta, Apr 07 2013
a(9) > 2*10^5. - Robert Price, Jan 21 2014
MATHEMATICA
Do[ If[ PrimeQ[6^n - n], Print[n] ], {n, 2500} ]
Select[Range[4000], PrimeQ[(6^# - #)] &] (* Vincenzo Librandi, Sep 29 2012 *)
PROG
(PARI) is(n)=ispseudoprime(6^n-n) \\ Charles R Greathouse IV, Feb 20 2017
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Robert G. Wilson v, Jan 04 2001
EXTENSIONS
a(6) from Vincenzo Librandi, Sep 29 2012
a(7) from Giovanni Resta, Apr 07 2013
a(8) from Robert Price, Jan 21 2014
a(9) from Ryan Propper, Dec 11 2022
STATUS
approved