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 A104607 #2 Mar 30 2012 17:31:12
%S A104607 1,1,1,0,1,1,1,1,2,1,2,0,1,1,0,1,1,2,0,0,1,2,0,1,1,0,0,0,1,1,1,1,2,1,
%T A104607 1,2,0,0,2,2,1,2,1,2,2,2,0,1,1,1,1,0,1,1,0,0,1,1,0,1,2,1,2,2,1,1,2,2,
%U A104607 1,2,0,1,2,2,2,0,2,2,1,0,2,2,2,0,1,2,2,2,2,1,1,0,1,1,2,0,1,1,0,2,0,0,0,1,1
%N A104607 Write the natural numbers in base 3 in a triangle with k digits in the k-th row, as shown below. Sequence gives the leading diagonal.
%C A104607 1
%C A104607 21
%C A104607 011
%C A104607 1220
%C A104607 21221
%C A104607 001011...
%t A104607 t = Flatten[IntegerDigits[Range[1000], 3]]; t[[Table[n(n + 1)/2, {n, 105}]]]
%Y A104607 Cf. A104606, A104608, A104609, A104610, A104611, A104612, A104613, A091425, A104614, A104615, A104616, A104617, A104618, A104619, A104620.
%K A104607 base,nonn
%O A104607 1,9
%A A104607 _Robert G. Wilson v_, Mar 16 2005