login
A228922
Numbers n such that (19^n + 2^n)/21 is prime.
0
5, 13, 41, 43, 83, 139, 557, 863, 1051, 4003
OFFSET
1,1
COMMENTS
All terms are primes.
a(11) > 10^5.
MATHEMATICA
Select[Prime[Range[1, 100000]], PrimeQ[(19^# + 2^#)/21]&]
PROG
(PARI) is(n)=ispseudoprime((19^n+2^n)/21) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Robert Price, Sep 08 2013
STATUS
approved