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 A036946 #16 Mar 09 2020 09:12:00
%S A036946 5,0,557,5557,57557,555557,5555777,55555777,555557557,5555555557,
%T A036946 55555555777,555555575557,5555555757757,55555555575757,
%U A036946 555555555555557,5555555555557577,55555555555777777,555555555557557757,5555555555555557577,55555555555575755777
%N A036946 Smallest n-digit prime containing only the digits 5 and 7, or 0 if no such prime exists.
%H A036946 Jinyuan Wang, <a href="/A036946/b036946.txt">Table of n, a(n) for n = 1..500</a>
%t A036946 Flatten[Join[{5,0},Table[Select[FromDigits/@(Join[#,{7}]&/@Tuples[ {5,7},n]), PrimeQ,1],{n,2,20}]]] (* _Harvey P. Dale_, Mar 08 2013 *)
%Y A036946 Cf. A020467, A036229, A036320.
%K A036946 nonn,base
%O A036946 1,1
%A A036946 _Patrick De Geest_, Jan 04 1999
%E A036946 More terms from _Harvey P. Dale_, Mar 08 2013