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 A073030 #3 May 10 2013 12:45:03
%S A073030 1,11,101,1111,10001,111111,1010101,11011011,101000101,1111111111,
%T A073030 10001010001,111111111111,1010100010101,11010011001011,
%U A073030 101010101010101,1111111111111111,10001010001010001,111111111111111111
%N A073030 Sum_{k=1..n, gcd(n,k) = 1} 10^(k-1).
%C A073030 A054431 is concatenation of a(n).
%Y A073030 Cf. A054431, A054432.
%K A073030 nonn
%O A073030 2,2
%A A073030 _Vladeta Jovovic_, Aug 15 2002