A228922 Numbers n such that (19^n + 2^n)/21 is prime.

5, 13, 41, 43, 83, 139, 557, 863, 1051, 4003

Offset

1,1

Comments

All terms are primes.

a(11) > 10^5.

Links

Table of n, a(n) for n=1..10.

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

Cf. A057185, A128075, A224507, A225191.

Sequence in context: A337339 A337336 A121872 * A025490 A216824 A230812

Adjacent sequences: A228919 A228920 A228921 * A228923 A228924 A228925

Keyword

nonn,hard,more

Author

Robert Price, Sep 08 2013

Status

approved