A227049 Numbers k such that (15^k + 4^k)/19 is prime.

3, 31, 157, 239, 1553, 5521, 25561

Offset: 1

Author

Robert Price, Jun 29 2013

Keywords

• hard
• nonn
• more

Comments

All terms are primes.

a(8) > 10^5.

Crossrefs

Cf. A057181, A128071, A128342, A213176, A224501, A221637.

Programs

Mathematica

Select[ Prime[ Range[1, 100000] ], PrimeQ[ (15^# + 4^#)/19 ]& ]

PARI

is(n)=ispseudoprime((15^n+4^n)/19) \\ Charles R Greathouse IV, Jun 06 2017