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 A216179 #8 Mar 16 2013 14:20:13
%S A216179 13,103,1003,10003,100003,1000003,10000003,100000003,1000000003,
%T A216179 10000000003,100000000003,1000000000003,10000000000003,
%U A216179 100000000000003,1000000000000003,10000000000000003,100000000000000003,1000000000000000003,10000000000000000003
%N A216179 a(n) = 10^n + 3.
%C A216179 1 followed by n - 1 0's followed by 3
%H A216179 Markus Tervooren, <a href="http://factordb.com/index.php?query=10^x%2B3">Factorizations of 1(0)w3</a>
%F A216179 a(n) = 10a(n - 1) - 27 with n > 1, a(1) = 13.
%t A216179 Table[10^n + 3, {n, 1, 19}]
%t A216179 NestList[10# - 27 &, 13, 18]
%Y A216179 Cf. A049054.
%K A216179 nonn,easy
%O A216179 1,1
%A A216179 _Ivan Panchenko_, Mar 10 2013