A082182 - OEIS

A082182

Numbers k such that (5^k - 2^k)/3 is prime.

2, 5, 7, 13, 19, 37, 59, 67, 79, 307, 331, 599, 1301, 12263, 12589, 18443, 20149, 27983, 281807, 656657, 795829, 832151

COMMENTS

No other terms less than 100000. - Robert Price, Apr 06 2012

All terms are primes. Some of the results were computed using the PrimeFormGW (PFGW) primality-testing program. - Hugo Pfoertner, Nov 14 2019

No other terms less than 1000000. - Jon Grantham, Jul 29 2023

EXAMPLE

a(1)=2 because (5^2 - 2^2)/3 = (25 - 4)/3 = 7 is a prime.

PROG

(PARI) forprime(p=2, 1e4, if(ispseudoprime((5^p-2^p)/3), print1(p", "))) \\ Charles R Greathouse IV, Jul 16 2011

EXTENSIONS

a(17) from Herman Jamke (hermanjamke(AT)fastmail.fm), May 03 2007