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 A216812 #5 Sep 18 2012 13:09:53 %S A216812 2,2,222,20,20,222,222222,200,222222222,20,2222222222,2220, %T A216812 222222222222,222222,2220,2000,2222222222222222,222222222, %U A216812 222222222222222222,20,222222 %N A216812 Smallest positive number divisible by n whose decimal expansion has the form 22...200...0. %F A216812 If n=3^k, a(n)=2(10^n-1)/9. For all n, a(n) <= 2(10^n-1)/9. %F A216812 a(2^k)= 2*10^(k-1). %F A216812 If p=prime, a(p) = 2(10^(p-1)-1)/9. %Y A216812 Cf. A078241, A216481. %K A216812 nonn,base %O A216812 1,1 %A A216812 _N. J. A. Sloane_, Sep 18 2012