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 A036940 #13 Mar 09 2020 09:12:53
%S A036940 3,43,433,3343,33343,333433,3333433,34333333,333334333,3333334343,
%T A036940 33333333343,333333343333,3333333333433,33333333433333,
%U A036940 333333333334343,3333333333333343,33333333333433433,333333333333334343
%N A036940 Smallest n-digit prime containing only digits 3 and 4, or 0 if no such prime exists.
%H A036940 Jinyuan Wang, <a href="/A036940/b036940.txt">Table of n, a(n) for n = 1..500</a>
%t A036940 Table[SelectFirst[FromDigits/@Tuples[{3,4},n],PrimeQ],{n,18}] (* The program uses the SelectFirst function from Mathematica version 10 *) (* _Harvey P. Dale_, May 29 2015 *)
%Y A036940 Cf. A020461, A036229, A036314.
%K A036940 nonn,base
%O A036940 1,1
%A A036940 _Patrick De Geest_, Jan 04 1999