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 A051820 #4 Jun 11 2014 17:24:23
%S A051820 1,4,25,180,1640,17678,213761,2572363,28717151,295374892,2863710220,
%T A051820 27059835840,257084859669,2498594395926,24825380748687,249116120158421
%N A051820 Number of n-digit numbers with nonzero multiplicative digital root 9.
%D A051820 William Mayne, sci.math, Jun 15 1991
%F A051820 # { i : 10^(n-1) < i < 10^n and A051802(i)=9 }
%Y A051820 Cf. A051802, A051811, A051829.
%K A051820 nonn,base,hard
%O A051820 1,2
%A A051820 _Dan Hoey_, Dec 09 1999