A213073 Numbers n such that (7^n - 4^n)/3 is prime.

2, 5, 11, 61, 619, 2879, 2957, 24371, 69247, 376463, 571199, 624803

Offset: 1

Author

Robert Price, Jun 04 2012

Keywords

• hard
• more
• nonn

Comments

All terms are primes.

Next term > 10^6.

Links

• Jon Grantham and Andrew Granville, Fibonacci primes, primes of the form 2^n-k and beyond, arXiv:2307.07894 [math.NT], 2023.

Crossrefs

Cf. A128344, A128024, A059802.

Programs

Mathematica

k=7; Do[p=Prime[n]; f=(k^p-4^p)/(k-4); If[ PrimeQ[f], Print[p] ], {n, 1, 100}]

PARI

is(n)=ispseudoprime((7^n-4^n)/3) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(10)-a(12) from Jon Grantham, Jul 29 2023