A228130 Numbers n such that (18^n + 5^n)/23 is prime.

61, 227, 233, 239, 613, 2213, 7507, 13691

Offset: 1

Author

Robert Price, Aug 11 2013

Keywords

• hard
• more
• nonn

Comments

All terms are primes.

a(9) > 10^5.

Crossrefs

Cf. A057184, A128353, A225397, A227046.

Programs

Mathematica

k=18; Do[p=Prime[n]; f=(k^p+5^p)/(k+5); If[ PrimeQ[f], Print[p] ], {n, 1, 9592}]

PARI

is(n)=ispseudoprime((18^n+5^n)/23) \\ Charles R Greathouse IV, Jun 13 2017