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%I #9 Jan 27 2020 01:46:32
%S 1,8,572,4778,12884
%N Numbers k such that (5^k + k)/3 is prime.
%C a(6) > 20065. - _Jinyuan Wang_, Jan 27 2020
%t Do[ If[ PrimeQ[ (5^n + n)/3 ], Print[ n ] ], {n, 1, 5000} ]
%o (PARI) is(n)=ispseudoprime((5^n+n)/3) \\ _Charles R Greathouse IV_, Jun 13 2017
%K nonn,more
%O 1,2
%A _Robert G. Wilson v_, Nov 17 2000
%E a(5) from _Jinyuan Wang_, Jan 27 2020
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