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 A096209 #25 Jun 15 2025 16:56:01
%S A096209 109,10999999999,1099999999999,1099999999999999999,
%T A096209 109999999999999999999999,1099999999999999999999999999999,
%U A096209 10999999999999999999999999999999999999
%N A096209 Primes of the form 10 followed by 9's only.
%C A096209 Or, primes of the form 10^k + 10^(k-1) - 1.
%C A096209 Number of 9's in a(n) is given by A111391(n). - _Daniel Starodubtsev_, Jan 06 2020
%F A096209 a(n) = 11*10^A111391(n) - 1 = A198700(A111391(n)). - _Elmo R. Oliveira_, Jun 14 2025
%t A096209 t = {}; Do[m = n; p = 10^(n + 1) + (10^n - 1); If[PrimeQ[p], AppendTo[t, p]], {n, 165}]; t (* _Robert G. Wilson v_ *)
%o A096209 (PARI) f(n) = for(x=1,n,y=10^x+10^(x-1)-1;if(ispseudoprime(y),print1(y", ")))
%Y A096209 Cf. A111391, A113628, A113629, A113630.
%Y A096209 Primes in A198700.
%K A096209 base,nonn
%O A096209 1,1
%A A096209 _Cino Hilliard_, Jul 28 2004
%E A096209 Entry revised by _N. J. A. Sloane_, Apr 01 2006