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 A036936 #14 May 26 2020 15:50:40
%S A036936 0,11,191,1999,11119,111119,1111991,11111119,111111199,1111111919,
%T A036936 11111111911,111111199919,1111111119919,11111111119111,
%U A036936 111111111119119,1111111111111999,11111111111111119,111111111111191111
%N A036936 Smallest n-digit prime containing only digits 1 and 9, or 0 if no such prime exists.
%H A036936 Jinyuan Wang, <a href="/A036936/b036936.txt">Table of n, a(n) for n = 1..500</a>
%t A036936 Table[SelectFirst[FromDigits/@Tuples[{1,9},n],PrimeQ],{n,20}]/. Missing["NotFound"]->0 (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, May 26 2020 *)
%Y A036936 Cf. A020457, A036229, A036309.
%K A036936 nonn,base
%O A036936 1,2
%A A036936 _Patrick De Geest_, Jan 04 1999