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%I #11 Dec 21 2019 15:11:17
%S 1,3,4,7,132,253,9040,21888
%N Numbers k such that 2*7^k - 3 is prime.
%C a(9) > 27376. - _Jinyuan Wang_, Dec 21 2019
%t Do[ If[ PrimeQ[ 2*7^n - 3 ], Print[n] ], {n, 1, 6000} ]
%o (PARI) is(n)=ispseudoprime(2*7^n-3) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y Cf. A059041 (3*7^k+2 is prime).
%K nonn,more
%O 1,2
%A _Robert G. Wilson v_, Feb 12 2001
%E a(7)-a(8) from _Jinyuan Wang_, Dec 21 2019
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