A224691 Numbers n such that (13^n - 4^n)/9 is prime.

2, 5, 19, 109, 157, 8521, 26017, 26177

Offset: 1

Author

Robert Price, Apr 15 2013

Keywords

• nonn
• hard
• more

Comments

All terms are prime.

a(9) > 10^5.

Crossrefs

Cf. A004063, A028491, A057468, A059801, A121877, A128024, A128025, A128026, A128027, A128028, A128029, A128030, A128031, A128032, A210506, A128347.

Programs

Mathematica

Select[Prime[Range[1, 100000]], PrimeQ[(13^# - 4^#)/9]&]

PARI

is(n)=ispseudoprime((13^n-4^n)/9) \\ Charles R Greathouse IV, Jun 13 2017