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 A125998 #4 Mar 31 2012 13:21:13
%S A125998 12,13,28,29,76,77,92,93,524,525,540,541,588,589,604,605,2060,2061,
%T A125998 2076,2077,2124,2125,2140,2141,2572,2573,2588,2589,2636,2637,2652,
%U A125998 2653,4108,4109,4124,4125,4172,4173,4188,4189,4620,4621,4636,4637
%N A125998 A106486-encodings of combinatorial games equivalent to game {1|1}.
%C A125998 These are codes for games which belong to the same equivalence class as the game {1|1}, the impartial game 1*.
%H A125998 A. Karttunen, <a href="/A126000/a126000.scm.txt">Scheme-program for computing this sequence.</a>
%e A125998 Game {1|1} is encoded as 2^(2*1) + 2^(1+2*1) = 12, thus 12 is the first term of this sequence. Also 13 belongs into this sequence, as it encodes game {0,1|1}, where, as the option 0 is dominated by option 1, the former can be deleted, resulting the same game {1|1}.
%Y A125998 Row 8 of A126000.
%K A125998 nonn
%O A125998 1,1
%A A125998 _Antti Karttunen_, Dec 18 2006