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%I #16 Jul 11 2024 18:52:08
%S 0,1,2,14,29,38,40,59,62,64,76,80,101,491,1024,1814,1826,13733,50516
%N Numbers k such that (10*7^k -1)/3 is prime.
%C No further terms through k = 5000. - _Harvey P. Dale_, Jan 09 2016
%C a(19) > 20941. - _Jinyuan Wang_, Dec 27 2019
%t Do[ If[ PrimeQ[ (10*7^n -1)/3 ], Print[ n ] ], {n, 0, 2500} ]
%t Select[Range[0,1900],PrimeQ[(10*7^#-1)/3]&] (* _Harvey P. Dale_, Jan 09 2016 *)
%o (PARI) is(n)=ispseudoprime((10*7^n-1)/3) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y Cf. A057437.
%K nonn,more
%O 1,3
%A _Robert G. Wilson v_, Sep 09 2000
%E a(18) from _Jinyuan Wang_, Dec 27 2019
%E a(19) from _Michael S. Branicky_, Jul 11 2024