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 A138711 #6 Nov 21 2013 12:49:20
%S A138711 1,0,0,0,1,1,1,1,1,1,0,0,0,0,0,0,0,0,0,0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
%T A138711 1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,1,1,1,1,1,1,1,1,1,1,
%U A138711 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1
%N A138711 n-th run has length n-th positive triangular number, with digits 0 and 1 only, starting with 1.
%e A138711 .n ..... Run ............................... Length
%e A138711 .1 ..... 1 ................................. 1
%e A138711 .2 ..... 0,0,0 ............................. 3
%e A138711 .3 ..... 1,1,1,1,1,1........................ 6
%e A138711 .4 ..... 0,0,0,0,0,0,0,0,0,0 ............... 10
%e A138711 .5 ..... 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1 ..... 15
%t A138711 Flatten[Table[Join[PadRight[{},(n(n+1))/2,1],PadRight[{},((n+1)(n+2))/2, 0]],{n,1,7,2}]] (* _Harvey P. Dale_, Dec 11 2011 *)
%Y A138711 Cf. A000217, A057211, A138149, A138709.
%K A138711 easy,nonn
%O A138711 1,1
%A A138711 _Omar E. Pol_, Mar 29 2008