A181139 - OEIS

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A181139

Numbers k such that R(k)^3 + R(k)^2 + 1 is prime, where R(k) = (10^k-1)/9.

%I #13 Mar 23 2024 10:42:30

%S 1,2,3,9,41,99,1863,4019,8925

%N Numbers k such that R(k)^3 + R(k)^2 + 1 is prime, where R(k) = (10^k-1)/9.

%t okQ[n_]:=Module[{x=FromDigits[PadRight[{},n,1]]},PrimeQ[x^3+x^2+1]]; Select[Range[5000],okQ] (* _Harvey P. Dale_, Nov 04 2011 *)

%K nonn,hard,more

%O 1,2

%A _Jason Earls_, Oct 06 2010

%E a(9) from _Michael S. Branicky_, Mar 22 2024