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 A038805 #5 May 19 2013 12:18:42
%S A038805 1,4,9,21,24,34,56,66,92,100,112,117,135,180,260,349,387,393,411,574,
%T A038805 617,787,1209
%N A038805 Difference between last prime < 10^n and 10^n is a record high.
%e A038805 For a(19)=411, the difference is 4433 and no other n <= 540 exceeds that difference.
%t A038805 PrevPrim[n_] := Block[{k = n - 1}, While[ !PrimeQ[k], k-- ]; k]; d = 0; k = 1; Do[ While[f = 10^k - PrevPrim[10^k]; d >= f, k++ ]; d = f; Print[k], {n, 1, 50}]
%Y A038805 Cf. A033874.
%K A038805 base,nonn
%O A038805 1,2
%A A038805 _Jeff Burch_
%E A038805 Edited and extended by _Robert G. Wilson v_, Jun 18 2002
%E A038805 a(23) from _Robert G. Wilson v_, Jan 10 2007