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A128349
Numbers k such that (13^k - 5^k)/8 is prime.
18
5, 19, 71, 197, 659, 22079, 61949
OFFSET
1,1
COMMENTS
All terms are primes.
a(8) > 10^5. - Robert Price, Mar 05 2013
MATHEMATICA
k=13; Do[p=Prime[n]; f=(k^p-5^p)/(k-5); If[ PrimeQ[f], Print[p] ], {n, 1, 100}]
PROG
(PARI) is(n)=isprime((13^n-5^n)/8) \\ Charles R Greathouse IV, Feb 17 2017
KEYWORD
hard,more,nonn
AUTHOR
Alexander Adamchuk, Feb 27 2007
EXTENSIONS
a(6)-a(7) from Robert Price, Mar 05 2013
STATUS
approved