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Numbers k such that (8^k + 7^k)/15 is prime.
16

%I #14 Nov 01 2018 21:32:20

%S 7,13,31,43,269,353,383,619,829,877,4957,5711,8317,21739,24029,38299

%N Numbers k such that (8^k + 7^k)/15 is prime.

%C Terms 21739 and 24029 were found by Lelio R. Paula in February and April 2009. Term 38299 was found by Jean-Louis Charton in October 2010 corresponding to a probable prime with 34587 digits.

%C a(17) > 10^5. - _Robert Price_, Dec 29 2012

%H <a href="http://www.primenumbers.net/prptop/searchform.php?form=%288%5En%2B7%5En%29%2F15&amp;action=Search">Top probable primes of form (8^n+7^n)/15</a>

%o (PARI) is(n)=isprime((8^n+7^n)/15) \\ _Charles R Greathouse IV_, Feb 17 2017

%Y See also A062574.

%K hard,nonn

%O 1,1

%A _Jean-Louis Charton_, Oct 06 2010