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 A229889 #10 Oct 04 2013 07:06:36 %S A229889 1,1,1,1,1,1,1,1,1,1,9,45,165,495,1287,3003,6435,12870,207350,1782638, %T A229889 10852478,52422578,213586658,762311978,2445069626,7177825511, %U A229889 167072419775,2041472747275,17401832788275,116094500641665,645070724513865,3103383925397925 %N A229889 Number of 8 up, 8 down permutations of [n]. %H A229889 Alois P. Heinz, <a href="/A229889/b229889.txt">Table of n, a(n) for n = 0..200</a> %e A229889 a(9) = 1: 123456789. %p A229889 b:= proc(u, o, t) option remember; `if`(u+o=0, 1, add(`if`(t=8, %p A229889 b(o-j, u+j-1, 1), b(u+j-1, o-j, t+1)), j=1..o)) %p A229889 end: %p A229889 a:= n-> b(0, n, 0): %p A229889 seq(a(n), n=0..35); %Y A229889 Column k=8 of A229892. %K A229889 nonn,eigen %O A229889 0,11 %A A229889 _Alois P. Heinz_, Oct 02 2013