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 A036950 #14 Mar 09 2020 12:27:34 %S A036950 7,79,797,0,77797,777977,7777997,77779799,777777799,7777779799, %T A036950 77777779979,777777779777,7777777779977,77777777777977, %U A036950 777777777779797,7777777777797799,77777777777777797,777777777777797977 %N A036950 Smallest n-digit prime containing only the digits 7 and 9, or 0 if no such prime exists. %H A036950 Jinyuan Wang, <a href="/A036950/b036950.txt">Table of n, a(n) for n = 1..500</a> %Y A036950 Cf. A020471, A036229, A036324. %K A036950 nonn,base %O A036950 1,1 %A A036950 _Patrick De Geest_, Jan 04 1999