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 A083909 #5 Jul 25 2016 10:59:28
%S A083909 9,990,99900,9999000,999990000,99999900000,9999999000000,
%T A083909 999999990000000,99999999900000000,9999999999000000000,
%U A083909 999999999990000000000,99999999999900000000000,9999999999999000000000000,999999999999990000000000000,99999999999999900000000000000
%N A083909 Numbers of the form 10^(m-k)*(10^(m+k+1)-10^k), m, k >= 0.
%t A083909 Table[FromDigits[Join[PadRight[{},n,9],PadRight[{},n-1,0]]],{n,15}] (* _Harvey P. Dale_, Jul 25 2016 *)
%Y A083909 Cf. A006516, A079598.
%K A083909 easy,nonn
%O A083909 1,1
%A A083909 _Marco Matosic_, Jun 19 2003
%E A083909 More terms from _Harvey P. Dale_, Jul 25 2016