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 A138794 #4 Jan 04 2013 14:53:51
%S A138794 20,300,4000,50000,600000,7000000,80000000,900000000,1000000000,
%T A138794 1100000000000,210000000000000,31000000000000000,4100000000000000000,
%U A138794 510000000000000000000,61000000000000000000000
%N A138794 a(n) = A138793(n+1)-A138793(n).
%C A138794 First differences of A138793
%F A138794 a(n) = A138793(n+1)-A138793(n)
%t A138794 b = {}; a = {}; Do[w = RealDigits[n]; w = First[w]; Do[AppendTo[a, w[[k]]], {k, 1, Length[w]}]; p = FromDigits[Reverse[a]]; AppendTo[b, p], {n, 1, 31}]; c = {}; Do[AppendTo[c, b[[n + 1]] - b[[n]]], {n, 1, Length[b] - 1}]; c (*Artur Jasinski*)
%Y A138794 Cf. A000422, A116504, A007908, A116505, A104759, A138789, A138790, A138793, A075019, A075020, A075021, A075022.
%K A138794 nonn,base
%O A138794 1,1
%A A138794 _Artur Jasinski_, Mar 30 2008