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 A036930 #11 Mar 09 2020 09:12:28
%S A036930 3,11,113,3313,11113,113111,1111333,11111131,111111113,1111113313,
%T A036930 11111111113,111111133333,1111111111333,11111111113133,
%U A036930 111111111113113,1111111111313131,11111111111131333,111111111111111131
%N A036930 Smallest n-digit prime containing only digits 1 and 3, or 0 if no such prime exists.
%H A036930 Jinyuan Wang, <a href="/A036930/b036930.txt">Table of n, a(n) for n = 1..500</a>
%t A036930 Flatten[Table[Select[FromDigits/@Tuples[{1,3},n],PrimeQ,1],{n,18}]] (* _Harvey P. Dale_, Jul 23 2012 *)
%Y A036930 Cf. A020451, A036229, A036303.
%K A036930 nonn,base
%O A036930 1,1
%A A036930 _Patrick De Geest_, Jan 04 1999
%E A036930 Corrected by _Harvey P. Dale_, Jul 23 2012