A128346 - OEIS

A128346

Numbers k such that (9^k - 5^k)/4 is prime.

3, 11, 17, 173, 839, 971, 40867, 45821, 147503

OFFSET

1,1

COMMENTS

All terms are primes.

a(9) > 10^5. - Robert Price, Jan 19 2013

a(10) > 10^6. - Jon Grantham, Jul 29 2023

LINKS

Jon Grantham and Andrew Granville, Fibonacci primes, primes of the form 2^n-k and beyond, arXiv:2307.07894 [math.NT], 2023.

MATHEMATICA

k=9; Do[p=Prime[n]; f=(k^p-5^p)/(k-5); If[ PrimeQ[f], Print[p] ], {n, 1, 100}]

PROG

(PARI) is(n)=isprime((9^n-5^n)/4) \\ Charles R Greathouse IV, Feb 17 2017

CROSSREFS

KEYWORD

hard,more,nonn

AUTHOR

EXTENSIONS

a(7)-a(8) from Robert Price, Jan 19 2013

a(8) corrected by Robert Price, Jan 20 2013

a(9) from Jon Grantham, Jul 29 2023

STATUS

approved