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 A036938 #12 Mar 09 2020 09:12:12 %S A036938 2,0,227,2777,22277,272227,2227727,22227277,222222227,2222222777, %T A036938 22222222277,222222272777,2222222227727,22222222777277, %U A036938 222222222222227,2222222222227727,22222222222227227,222222222227227727 %N A036938 Smallest n-digit prime containing only digits 2 and 7, or 0 if no such prime exists. %H A036938 Jinyuan Wang, <a href="/A036938/b036938.txt">Table of n, a(n) for n = 1..500</a> %Y A036938 Cf. A020459, A036229, A036312. %K A036938 nonn,base %O A036938 1,1 %A A036938 _Patrick De Geest_, Jan 04 1999