A128335 - OEIS
A128335
Numbers k such that (4^k + 5^k)/9 is prime.
31
5, 7, 19, 29, 61, 137, 883, 1381, 1823, 5227, 25561, 29537, 300893
OFFSET
1,1
COMMENTS
All terms are primes.
LINKS
Henri Lifchitz and Renaud Lifchitz, Top probable primes of the form (5^p+4^p)/9
MATHEMATICA
k=4; Do[p=Prime[n]; f=(k^p+5^p)/(k+5); If[ PrimeQ[f], Print[p] ], {n, 1, 100}]
PROG
(PARI) forprime(p=3, 1e4, if(ispseudoprime((5^p+4^p)/9), print1(p", "))) \\ Charles R Greathouse IV, Jul 16 2011
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
Alexander Adamchuk, Feb 27 2007
EXTENSIONS
3 more terms from Ryan Propper, Feb 06 2008
Two more terms from Ryan Propper, May 02 2010
New term 300893 found by Jean-Louis Charton in November 2011 corresponding to a probable prime with 210315 digits.
STATUS
approved