A218373 Numbers n such that (7^n + 4^n)/11 is prime.

3, 5, 19, 41, 47, 8231, 33931, 43781, 50833, 53719, 67211

Offset: 1

Author

Robert Price, Oct 27 2012

Keywords

• hard
• more
• nonn

Comments

All terms are primes.

a(11) > 10^5

Crossrefs

Cf. A128335, A128067, A128337.

Programs

Mathematica

Do[ p=Prime[n]; f=(7^p+4^p)/11; If[ PrimeQ[f], Print[p]], {n, 1, 9592} ]

PARI

is(n)=ispseudoprime((7^n+4^n)/11) \\ Charles R Greathouse IV, Jun 13 2017