OFFSET
1,1
COMMENTS
a(7) > 20000. - Giovanni Resta, Apr 09 2013
a(10) > 2*10^5. - Robert Price, Mar 12 2014
MATHEMATICA
Select[Range[1000], PrimeQ[9^# - #] &] (* Alonso del Arte, Apr 11 2013 *)
PROG
(PARI) is(n)=ispseudoprime(9^n-n) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Alex Ratushnyak, Apr 08 2013
EXTENSIONS
a(6) from Giovanni Resta, Apr 09 2013
a(7)-a(9) from Robert Price, Mar 12 2014
STATUS
approved