A228558 Numbers k such that (17^k + 4^k)/21 is prime.

13, 61, 67, 107, 383, 647, 3571, 37967

Offset

1,1

Comments

Conjecture: All terms are prime.

a(9) > 10^5.

Links

Table of n, a(n) for n=1..8.

Mathematica

Select[ Prime[ Range[1, 100000] ], PrimeQ[ (17^# + 4^#)/21 ]& ]

Prog

(PARI) is(n)=ispseudoprime((17^n+4^n)/21) \\ Charles R Greathouse IV, May 22 2017

Crossrefs

Cf. A227049, A228225, A227046.

Sequence in context: A343538 A305250 A304542 * A316550 A244923 A146764

Adjacent sequences: A228555 A228556 A228557 * A228559 A228560 A228561

Keyword

hard,nonn,more

Author

Robert Price, Aug 25 2013

Status

approved