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 A114880 #5 Oct 19 2017 03:14:59 %S A114880 1,212,2111,22222,21112,222111222,212121212,22112121,212221222212, %T A114880 2221221221222,222222222222222,22222222222222222,1121212211122121211, %U A114880 2121212121212121212,112221112211111121,21111111111111111111 %N A114880 a(n) is the largest base-3 string such that the n-th number coprime to 3 does not divide any substring of a(n). %e A114880 a(3) = 212 (base three) because the 3rd number coprime to 4 is 4, and 4 does not divide any substring of a(3). %K A114880 nonn,base %O A114880 2,2 %A A114880 _Don Reble_, Feb 20 2006