A128347 - OEIS
A128347
Numbers k such that (11^k - 5^k)/6 is prime.
26
5, 41, 149, 229, 263, 739, 3457, 20269, 98221
OFFSET
1,1
COMMENTS
All terms are primes.
a(10) > 10^5. - Robert Price, Jan 24 2013
MATHEMATICA
k=11; Do[p=Prime[n]; f=(k^p-5^p)/(k-5); If[ PrimeQ[f], Print[p] ], {n, 1, 100}]
PROG
(PARI) is(n)=isprime((11^n-5^n)/6) \\ Charles R Greathouse IV, Feb 17 2017
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
Alexander Adamchuk, Feb 27 2007
EXTENSIONS
a(7)-a(9) from Robert Price, Jan 24 2013
STATUS
approved