login
A224691
Numbers n such that (13^n - 4^n)/9 is prime.
1
2, 5, 19, 109, 157, 8521, 26017, 26177
OFFSET
1,1
COMMENTS
All terms are prime.
a(9) > 10^5.
MATHEMATICA
Select[Prime[Range[1, 100000]], PrimeQ[(13^# - 4^#)/9]&]
PROG
(PARI) is(n)=ispseudoprime((13^n-4^n)/9) \\ Charles R Greathouse IV, Jun 13 2017
KEYWORD
nonn,hard,more
AUTHOR
Robert Price, Apr 15 2013
STATUS
approved