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%I #13 Jul 10 2024 23:57:51
%S 0,1,2,3,5,9,11,15,33,38,239,419,441,486,5127,6953,6998,45609
%N Numbers k such that 2*7^k + 5 is prime.
%C a(18) > 33600. - _Jinyuan Wang_, Jan 23 2020
%t Do[ If[ PrimeQ[ 2*7^n + 5 ], Print[n] ], {n, 0, 6850} ]
%o (PARI) is(n)=ispseudoprime(2*7^n+5) \\ _Charles R Greathouse IV_, Jun 13 2017
%K nonn,more
%O 1,3
%A _Robert G. Wilson v_, Feb 12 2001
%E a(16)-a(17) from _Jinyuan Wang_, Jan 23 2020
%E a(18) from _Michael S. Branicky_, Jul 10 2024