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A128342
Numbers k such that (13^k + 5^k)/18 is prime.
23
13, 19, 31, 359, 487, 757, 761, 1667, 2551, 3167, 6829
OFFSET
1,1
COMMENTS
All terms are primes.
No other terms below 23600. - Max Alekseyev, Feb 01 2010
a(12) > 10^5. - Robert Price, Apr 30 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)/18) \\ Charles R Greathouse IV, Feb 17 2017
KEYWORD
hard,more,nonn
AUTHOR
Alexander Adamchuk, Feb 27 2007
EXTENSIONS
Four more terms from Max Alekseyev, Feb 01 2010
STATUS
approved