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%I #7 Jun 06 2017 14:35:01
%S 3,31,157,239,1553,5521,25561
%N Numbers n such that (15^n + 4^n)/19 is prime.
%C All terms are primes.
%C a(8) > 10^5.
%t Select[ Prime[ Range[1, 100000] ], PrimeQ[ (15^# + 4^#)/19 ]& ]
%o (PARI) is(n)=ispseudoprime((15^n+4^n)/19) \\ _Charles R Greathouse IV_, Jun 06 2017
%Y Cf. A057181, A128071, A128342, A213176, A224501, A221637.
%K hard,nonn,more
%O 1,1
%A _Robert Price_, Jun 29 2013
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