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 A104608 #2 Mar 30 2012 17:31:12
%S A104608 1,3,1,1,1,0,1,2,1,1,0,0,2,1,2,3,1,3,1,2,2,1,1,1,2,0,0,2,1,0,2,2,2,1,
%T A104608 0,2,0,0,3,3,2,2,0,1,1,0,1,0,1,1,1,1,1,1,1,2,3,2,1,1,2,2,3,1,1,3,2,0,
%U A104608 2,2,1,0,1,2,2,2,3,2,2,2,3,3,3,3,3,0,0,1,3,3,2,2,2,3,3,3,2,3,0,1,1,2,1,1,2
%N A104608 Write the natural numbers in base 4 in a triangle with k digits in the k-th row, as shown below. Sequence gives the leading diagonal.
%C A104608 1
%C A104608 23
%C A104608 101
%C A104608 1121
%C A104608 32021
%C A104608 222330...
%t A104608 t = Flatten[IntegerDigits[Range[1500], 4]]; t[[Table[n(n + 1)/2, {n, 105}]]]
%Y A104608 Cf. A104606, A104607, A104609, A104610, A104611, A104612, A104613, A091425, A104614, A104615, A104616, A104617, A104618, A104619, A104620.
%K A104608 base,nonn
%O A104608 1,2
%A A104608 _Robert G. Wilson v_, Mar 16 2005