A138931 - OEIS

%I #4 Dec 18 2018 16:33:57

%S 13,139,14251,1428571428571428571364245156301286091

%N Primes of the form (10^n-3^n)/7.

%C The next term is too large to include here.

%t a={};Do[p=(10^n-3^n)/7;If[PrimeQ[p],AppendTo[a,p]],{n,1,25^2}];a

%t Select[Table[(10^n-3^n)/7,{n,50}],PrimeQ] (* _Harvey P. Dale_, Dec 18 2018 *)

%Y Cf. A128026.

%K nonn

%O 1,1

%A _Vladimir Joseph Stephan Orlovsky_, May 16 2008