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 A143829 #6 Nov 11 2020 15:37:57
%S A143829 3,6,9,12,21,30,33,36,45,48,60,69,72,75,81,87,99,108,111,114,117,120,
%T A143829 123,126,129,153,165,168,174,177,183,201,204,207,222,234,243,252,267,
%U A143829 279,282,285,294,303,312,315,318,339,345,348,369,378,381,384,393,396
%N A143829 Numbers n such that 10n^2 - 1 is prime.
%t A143829 p = 10; a = {}; Do[k = p x^2 - 1; If[PrimeQ[k], AppendTo[a, x]], {x, 1, 1000}]; a
%t A143829 Select[Range[500],PrimeQ[10#^2-1]&] (* _Harvey P. Dale_, Nov 11 2020 *)
%o A143829 (PARI) is(n)=isprime(10*n^2-1) \\ _Charles R Greathouse IV_, Feb 17 2017
%Y A143829 A066436, A066049, A090686, A090684, A143826, A143827, A143828
%K A143829 nonn
%O A143829 1,1
%A A143829 _Artur Jasinski_, Sep 02 2008