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 A229888 #9 Oct 04 2013 07:05:39 %S A229888 1,1,1,1,1,1,1,1,1,8,36,120,330,792,1716,3432,48477,368797,2002429, %T A229888 8685469,31964725,103593205,303129685,6156709438,66139517554, %U A229888 498859498016,2961422519550,14715247475500,63593705003400,245316996896400,6498850067259615 %N A229888 Number of 7 up, 7 down permutations of [n]. %H A229888 Alois P. Heinz, <a href="/A229888/b229888.txt">Table of n, a(n) for n = 0..200</a> %e A229888 a(8) = 1: 12345678. %e A229888 a(9) = 8: 123456798, 123456897, 123457896, 123467895, 123567894, 124567893, 134567892, 234567891. %p A229888 b:= proc(u, o, t) option remember; `if`(u+o=0, 1, add(`if`(t=7, %p A229888 b(o-j, u+j-1, 1), b(u+j-1, o-j, t+1)), j=1..o)) %p A229888 end: %p A229888 a:= n-> b(0, n, 0): %p A229888 seq(a(n), n=0..35); %Y A229888 Column k=7 of A229892. %K A229888 nonn,eigen %O A229888 0,10 %A A229888 _Alois P. Heinz_, Oct 02 2013