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

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

Offset: 1

Author

Robert Price, Sep 08 2013

Keywords

• nonn
• hard
• more

Comments

All terms are primes.

a(11) > 10^5.

Crossrefs

Cf. A057185, A128075, A224507, A225191.

Programs

Mathematica

Select[Prime[Range[1, 100000]], PrimeQ[(19^# + 2^#)/21]&]

PARI

is(n)=ispseudoprime((19^n+2^n)/21) \\ Charles R Greathouse IV, Jun 13 2017