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 A020904 #8 Mar 30 2012 18:55:49 %S A020904 2,4,7,9,11,13,16,18,22,24,27,29,31,34,37,39,42,44,46,48,51,53,56,58, %T A020904 61,63,65,67,69,72,74,76,79,81,84,86,88,90,92,94,97,99,101,103,106, %U A020904 108,111,113,115,117,121,123,126,128,130,132,135,137,139,142 %N A020904 Positions of 2 in A020903; complement of A191777. %H A020904 C. Kimberling, <a href="http://faculty.evansville.edu/ck6/integer/fractals.html">Fractal sequences</a> %H A020904 C. Kimberling, <a href="http://matwbn.icm.edu.pl/ksiazki/aa/aa73/aa7321.pdf">Numeration systems and fractal sequences</a>, Acta Arithmetica 73 (1995) 103-117. %e A020904 A020903 starts 1,2,1,2,1,1,2,1,2,... in which 2 occupies positions 2, 4, 7, 9, 11,... (Positions refer to offset 1 in A020903). %t A020904 (See A020903.) %Y A020904 Cf. A020903, A191777. %K A020904 nonn %O A020904 1,1 %A A020904 _Clark Kimberling_