A181139 Numbers k such that R(k)^3 + R(k)^2 + 1 is prime, where R(k) = (10^k-1)/9.

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

Offset: 1

Author

Jason Earls, Oct 06 2010

Keywords

• nonn
• hard
• more

Programs

Mathematica

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

Extensions

a(9) from Michael S. Branicky, Mar 22 2024