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%I #17 Apr 30 2023 07:08:09
%S 2,4,16,24,32,40,120,124,144,172,186,376,700,1232,1264,2894,5054,
%T 14826,16498,18348,33416
%N Numbers k such that (5*3^k - 7)/2 is prime.
%C a(21) > 20000. - _Jinyuan Wang_, Jan 28 2020
%t Do[ If[ PrimeQ[ (5*3^n - 7)/2 ], Print[n] ], {n, 0, 10000} ]
%t Select[Range[5100],PrimeQ[(5*3^#-7)/2]&] (* _Harvey P. Dale_, Jul 15 2018 *)
%o (PARI) is(n)=ispseudoprime((5*3^n-7)/2) \\ _Charles R Greathouse IV_, Jun 13 2017
%o (Magma) [k: k in [0..1000] | IsPrime((5*3^k - 7) div 2)]; // _Jinyuan Wang_, Jan 28 2020
%Y Cf. A059621 ((5*3^k+7)/2 is prime).
%K nonn,more
%O 1,1
%A _Robert G. Wilson v_, Feb 19 2001
%E a(18)-a(20) from _Jinyuan Wang_, Jan 28 2020
%E a(21) from _Michael S. Branicky_, Apr 29 2023
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