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 A216481 #9 Sep 18 2012 13:13:35 %S A216481 2,2,222,-1,-1,222,222222,-1,222222222,-1,22,-1,222222,222222,-1,-1, %T A216481 2222222222222222,222222222,222222222222222222,-1,222222,22, %U A216481 2222222222222222222222,-1,-1,222222,222222222222222222222222222,-1,2222222222222222222222222222,-1,222222222222222,-1,222222,2222222222222222,-1,-1,222,222222222222222222,222222,-1,22222,222222 %N A216481 a(n) is the least multiple of n which uses only digit 2, or a(n) = -1 if no such multiple exists. %Y A216481 Cf. A004290, A078241, A079339, A181060, A181061, A216812. %K A216481 sign,base %O A216481 1,1 %A A216481 _V. Raman_, Sep 07 2012