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A128338
Numbers k such that (8^k + 5^k)/13 is prime.
17
7, 19, 167, 173, 223, 281, 21647
OFFSET
1,1
COMMENTS
All terms are primes.
a(8) > 10^5. - Robert Price, Jan 21 2013
MATHEMATICA
k=8; Do[p=Prime[n]; f=(k^p+5^p)/(k+5); If[ PrimeQ[f], Print[p] ], {n, 1, 100}]
PROG
(PARI) is(n)=isprime((8^n+5^n)/13) \\ Charles R Greathouse IV, Feb 17 2017
KEYWORD
hard,more,nonn
AUTHOR
Alexander Adamchuk, Feb 27 2007
EXTENSIONS
a(7) from Robert Price, Jan 21 2013
STATUS
approved