A225397 Numbers n such that (16^n + 5^n)/21 is prime.

31, 109, 373, 409, 619, 823, 1531, 6637, 70687

Offset

1,1

Comments

All terms are primes.

a(10) > 10^5.

Links

Table of n, a(n) for n=1..9.

Mathematica

k=16; Do[p=Prime[n]; f=(k^p+5^p)/(k+5); If[ PrimeQ[f], Print[p] ], {n, 1, 9592}]

Prog

(PARI) is(n)=ispseudoprime((16^n+5^n)/21) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Cf. A128340, A128341, A128342, A128343, A227046, A128073.

Sequence in context: A206526 A141877 A057230 * A142177 A281194 A063397

Adjacent sequences: A225394 A225395 A225396 * A225398 A225399 A225400

Keyword

hard,more,nonn

Author

Robert Price, Jul 25 2013

Status

approved