A128340 Numbers k such that (11^k + 5^k)/16 is prime.

7, 11, 181, 421, 2297, 2797, 4129, 4139, 7151, 29033

Offset: 1

Author

Alexander Adamchuk, Feb 27 2007

Keywords

• hard
• more
• nonn

Comments

All terms are primes.

a(11) > 10^5. - Robert Price, Feb 09 2013

Crossrefs

Cf. A057171, A082387, A122853, A128335, A128336, A128337, A128338, A128339, A128341, A128342, A128343.

Cf. A004061, A082182, A121877, A059802.

Cf. A062572, A128344, A128345, A128346, A128347, A128348, A128349, A128350, A128351, A128352, A128353, A128354.

Programs

Mathematica

k=11; Do[p=Prime[n]; f=(k^p+5^p)/(k+5); If[ PrimeQ[f], Print[p] ], {n,1,100}]

PARI

is(n)=isprime((11^n+5^n)/16) \\ Charles R Greathouse IV, Feb 17 2017

Extensions

a(5)-a(10) from Robert Price, Feb 09 2013