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 A072805 #5 Oct 15 2013 22:31:25
%S A072805 10,21,102,201,212,1011,1121,1202,2012,2111,2122,2221,10002,10211,
%T A072805 10222,11201,11212,12011,12121,20001,20012,20122,21002,21101,21211,
%U A072805 22021,22102,22212,100022,100202,101001,101111,102101,102112,110021
%N A072805 Primes of form 4k+3 written in base 3.
%e A072805 83 ~ 10002 in base 3.
%t A072805 Do[s=Prime[n]; If[Mod[s, 4]==3, Print[BaseForm[s, 3]]], {n, 1, 256}]
%Y A072805 Cf. A008713, A072803-A072807.
%K A072805 base,nonn
%O A072805 1,1
%A A072805 _Labos Elemer_, Jul 12 2002