This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A181139 #13 Mar 23 2024 10:42:30
%S A181139 1,2,3,9,41,99,1863,4019,8925
%N A181139 Numbers k such that R(k)^3 + R(k)^2 + 1 is prime, where R(k) = (10^k-1)/9.
%t A181139 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 A181139 nonn,hard,more
%O A181139 1,2
%A A181139 _Jason Earls_, Oct 06 2010
%E A181139 a(9) from _Michael S. Branicky_, Mar 22 2024