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 A129877 #5 Mar 30 2013 04:52:55
%S A129877 2,0,6,12,58,220,958,4184
%N A129877 Sequence i_{a_n} arising in enumeration of arrays of directed blocks (see Quaintance reference for precise definition), where i_n is A129876, a_n is A129878.
%D A129877 Jocelyn Quaintance, Combinatoric Enumeration of Two-Dimensional Proper Arrays, Discrete Math., 307 (2007), 1844-1864.
%F A129877 See Quaintance reference for generating functions that produce A129872-A129886.
%K A129877 nonn,more
%O A129877 1,1
%A A129877 _N. J. A. Sloane_, May 26 2007