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 A216478 #3 Sep 10 2012 23:23:43 %S A216478 1,2,12,12,-1,12,21,112,12222,-1,11,12,221,112,-1,112,221,12222,1121, %T A216478 -1,21,22,12121,2112,-1,1222,21222,112,12122,-1,11222,2112,1122,1122, %U A216478 -1,22212,111,12122,111111,-1,11111,12222,12212,2112,-1,122222,1222,2112,11221,-1,1122,21112,212,21222,-1,112,212211,12122,1121 %N A216478 a(n) is the least multiple of n which uses only digits 1 and 2. a(n) = -1 if no such multiple exists. %Y A216478 Cf. A004290, A079339, A181060, A181061. %K A216478 sign,base %O A216478 1,2 %A A216478 _V. Raman_, Sep 07 2012