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 A059622 Numbers k such that (5*3^k - 7)/2 is prime. 1

%I

%S 2,4,16,24,32,40,120,124,144,172,186,376,700,1232,1264,2894,5054,

%T 14826,16498,18348

%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

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Last modified September 22 02:48 EDT 2021. Contains 347605 sequences. (Running on oeis4.)